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Psychedex
Sources
40
4 strong · 30 moderate · 6 weak

Studies and references cited across this article, graded by evidence strength.

Claims checked
96
63verified5partial28inconclusive

Inconclusive means the cited source neither confirms nor refutes the claim — a lower-confidence badge, not an error.

Generated
Apr 24, 2026 · pipeline-v5
Values approved
84/84 (100%)

Data points an editor reviewed and accepted for publication.

01

Value Provenance

Dosing

oraltrace

FieldPublishedAI ProposedConfidence
Threshold15 mg15 mgmedium
Low30–60 mg30–60 mgmedium
Common60–120 mg60–120 mgmedium
Strong120–200 mg120–200 mgmedium
Heavy200+ mg200+ mgmedium
Editorial

Dose ranges derived from existing database values (community consensus) corroborated by clinical pharmacology. Standard therapeutic single dose is 15-60 mg (FDA labeling). Equianalgesic ratio of 10:1 codeine:morphine (100 mg codeine ~ 10 mg oral morphine). Bioavailability 50-60% after first-pass metabolism (Dahan et al. 2014). Doses above 120 mg exceed standard therapeutic recommendations and carry increased respiratory depression risk, particularly in CYP2D6 ultrarapid metabolizers.

Reasoning

Dose ranges derived from existing database values (community consensus) corroborated by clinical pharmacology. Standard therapeutic single dose is 15-60 mg (FDA labeling). Equianalgesic ratio of 10:1 codeine:morphine (100 mg codeine ~ 10 mg oral morphine). Bioavailability 50-60% after first-pass metabolism (Dahan et al. 2014). Doses above 120 mg exceed standard therapeutic recommendations and carry increased respiratory depression risk, particularly in CYP2D6 ultrarapid metabolizers.

Evidence basis: community_consensus_large

Duration

oral

FieldPublishedAI ProposedConfidence
Come uptrace1–2 hours1–2 hoursmedium
Editorial

Come-up of 1-2 hours from existing database values. Consistent with Tmax 1.0-1.4 hours — effects build through and beyond peak plasma concentration as morphine metabolite accumulates.

Reasoning

Come-up of 1-2 hours from existing database values. Consistent with Tmax 1.0-1.4 hours — effects build through and beyond peak plasma concentration as morphine metabolite accumulates.

Evidence basis: community_consensus_large

Onsettrace30–45 minutes30–45 minutesmedium
Editorial

Onset 30-45 minutes consistent with community reports and pharmacokinetic Tmax of 1.0-1.4 hours (Mohammed et al. 1993). Oral absorption >90% with BCS Class I designation (Dahan et al. 2014).

Reasoning

Onset 30-45 minutes consistent with community reports and pharmacokinetic Tmax of 1.0-1.4 hours (Mohammed et al. 1993). Oral absorption >90% with BCS Class I designation (Dahan et al. 2014).

Evidence basis: community_consensus_large

Peaktrace3–5 hours3–5 hoursmedium
Editorial

Peak duration 3-5 hours from existing database values. Sustained by morphine and M6G metabolite plasma levels. Consistent with t½ ~2.8 hours (Mohammed et al. 1993) — effects persist through ~1-2 half-lives.

Reasoning

Peak duration 3-5 hours from existing database values. Sustained by morphine and M6G metabolite plasma levels. Consistent with t½ ~2.8 hours (Mohammed et al. 1993) — effects persist through ~1-2 half-lives.

Evidence basis: community_consensus_large

Offsettrace2–4 hours2–4 hoursmedium
Editorial

Offset 2-4 hours from existing database values. Reflects gradual decline of morphine and metabolite plasma levels below pharmacodynamically active thresholds.

Reasoning

Offset 2-4 hours from existing database values. Reflects gradual decline of morphine and metabolite plasma levels below pharmacodynamically active thresholds.

Evidence basis: community_consensus_large

Totaltrace3–6 hours3–6 hoursmedium
Editorial

Total subjective duration 3-6 hours from existing database values. Consistent with parent compound t½ ~2.8 hours. Lower end reflects threshold/light doses; upper end reflects common-to-strong doses where M6G contribution extends effects.

Reasoning

Total subjective duration 3-6 hours from existing database values. Consistent with parent compound t½ ~2.8 hours. Lower end reflects threshold/light doses; upper end reflects common-to-strong doses where M6G contribution extends effects.

Evidence basis: community_consensus_large

After effectstrace2–4 hours2–4 hourslow
Editorial

Aftereffects 2-4 hours estimated. Residual sedation and gastrointestinal effects may persist beyond subjective experience. M6G metabolite may extend subtle effects in extensive metabolizers. No specific published data on codeine aftereffect duration.

Reasoning

Aftereffects 2-4 hours estimated. Residual sedation and gastrointestinal effects may persist beyond subjective experience. M6G metabolite may extend subtle effects in extensive metabolizers. No specific published data on codeine aftereffect duration.

Evidence basis: community_consensus_large

Safety

Toxicity Profiletrace

FieldPublishedAI ProposedConfidence
Acutemoderatemoderatehigh
Chronicmoderatemoderatehigh
Organs Affectedrespiratory, gastrointestinal, central_nervous_systemrespiratory, gastrointestinal, central_nervous_systemhigh
Editorial

Classified as moderate acute: codeine is less toxic than morphine at equianalgesic doses (Eddy et al. 1968) but has documented fatalities, particularly in CYP2D6 ultrarapid metabolizers (Kelly et al. 2012). Forensic TIAFT thresholds established from 1,444 consecutive autopsies (Frost et al. 2012). Chronic toxicity moderate: dependence is well-documented globally; gastrointestinal dysfunction is reliable; no direct organ toxicity from codeine itself.

Reasoning

Classified as moderate acute: codeine is less toxic than morphine at equianalgesic doses (Eddy et al. 1968) but has documented fatalities, particularly in CYP2D6 ultrarapid metabolizers (Kelly et al. 2012). Forensic TIAFT thresholds established from 1,444 consecutive autopsies (Frost et al. 2012). Chronic toxicity moderate: dependence is well-documented globally; gastrointestinal dysfunction is reliable; no direct organ toxicity from codeine itself.

Evidence basis: published_case_series

Dependence Profiletrace

FieldPublishedAI ProposedConfidence
Physicalmoderatemoderatehigh
Psychologicalmoderatemoderatehigh
Compulsive Redosingmoderatemoderatehigh
Dose Escalationmoderatemoderatehigh
Editorial

Physical and psychological dependence are both moderate, consistently described as less intense than morphine dependence (Eddy et al. 1968). Compulsive redosing is documented in OTC misuse literature (Bergin et al. 2015; Wells et al. 2018). The global OTC codeine dependence burden is well-established (Algarni et al. 2021).

Reasoning

Physical and psychological dependence are both moderate, consistently described as less intense than morphine dependence (Eddy et al. 1968). Compulsive redosing is documented in OTC misuse literature (Bergin et al. 2015; Wells et al. 2018). The global OTC codeine dependence burden is well-established (Algarni et al. 2021).

Evidence basis: published_case_series

Withdrawal Profiletrace

FieldPublishedAI ProposedConfidence
Severitymildmildmedium
Symptomsanxiety, agitation, muscle aches, insomnia, yawning, diaphoresis, lacrimation, rhinorrhea, nausea, vomiting, diarrhea, abdominal cramps, piloerection, tachycardiaanxiety, agitation, muscle aches, insomnia, yawning, diaphoresis, lacrimation, rhinorrhea, nausea, vomiting, diarrhea, abdominal cramps, piloerection, tachycardiamedium
FatalNoNomedium
Medical SupervisionNot requiredNot requiredmedium
Editorial

Codeine withdrawal is milder and shorter than morphine withdrawal (Eddy et al. 1968). Buprenorphine induction successful at 23.5 hours post-last-dose suggests withdrawal onset within 12-24 hours (Teixeira et al. 2025). Symptoms follow standard opioid withdrawal pattern.

Reasoning

Codeine withdrawal is milder and shorter than morphine withdrawal (Eddy et al. 1968). Buprenorphine induction successful at 23.5 hours post-last-dose suggests withdrawal onset within 12-24 hours (Teixeira et al. 2025). Symptoms follow standard opioid withdrawal pattern.

Evidence basis: published_case_series

Tolerance Profiletrace

FieldPublishedAI ProposedConfidence
Buildupmoderatemoderatemedium
Half-life5 days5 daysmedium
Full Reset10 days10 daysmedium
Cross-tolerancesmorphine, heroin, oxycodone, hydrocodone, fentanyl, tramadol, dihydrocodeinemorphine, heroin, oxycodone, hydrocodone, fentanyl, tramadol, dihydrocodeinemedium
Editorial

Tolerance buildup characterized as moderate based on opioid class pharmacology and codeine's lower potency relative to morphine (Eddy et al. 1968). Cross-tolerance with all mu-opioid agonists is confirmed by class pharmacology. Specific numerical tolerance values (5-day half-life, 10-day reset) are from existing database; no primary source confirmed in this review.

Reasoning

Tolerance buildup characterized as moderate based on opioid class pharmacology and codeine's lower potency relative to morphine (Eddy et al. 1968). Cross-tolerance with all mu-opioid agonists is confirmed by class pharmacology. Specific numerical tolerance values (5-day half-life, 10-day reset) are from existing database; no primary source confirmed in this review.

Evidence basis: community_consensus_large

Effects & Profile

Contraindications

FieldPublishedAI ProposedConfidence
age Children under 12 yearstraceabsoluteabsolutehigh
Editorial

FDA black box warning (2013) based on Kelly et al. 2012 case series documenting pediatric fatalities linked to CYP2D6 gene duplications.

Reasoning

FDA black box warning (2013) based on Kelly et al. 2012 case series documenting pediatric fatalities linked to CYP2D6 gene duplications.

other Post-tonsillectomy/adenoidectomytraceabsoluteabsolutehigh
Editorial

FDA black box warning based on pediatric fatality case reports (Kelly et al. 2012). Kaiser Permanente institutional protocol change (Luk et al. 2016).

Reasoning

FDA black box warning based on pediatric fatality case reports (Kelly et al. 2012). Kaiser Permanente institutional protocol change (Luk et al. 2016).

metabolic CYP2D6 ultrarapid metabolizer statustraceabsoluteabsolutehigh
Editorial

CYP2D6 UM status is directly linked to codeine fatalities (Kelly et al. 2012). Ethnic prevalence variation documented (Kim et al. 2025). Clinical outcomes data support association (St Sauver et al. 2017).

Reasoning

CYP2D6 UM status is directly linked to codeine fatalities (Kelly et al. 2012). Ethnic prevalence variation documented (Kim et al. 2025). Clinical outcomes data support association (St Sauver et al. 2017).

pregnancy breastfeeding Breastfeedingtracerelativerelativemedium
Editorial

FDA advisory based on 2009 Toronto case. Disputed by Zipursky & Juurlink 2020 critical reanalysis. Listed as relative due to scientific controversy.

Reasoning

FDA advisory based on 2009 Toronto case. Disputed by Zipursky & Juurlink 2020 critical reanalysis. Listed as relative due to scientific controversy.

respiratory Respiratory insufficiencytracerelativerelativehigh
Editorial

Standard opioid class contraindication supported by mechanism of action at brainstem respiratory centers. Well-established in opioid pharmacology literature (Stubhaug 2012).

Reasoning

Standard opioid class contraindication supported by mechanism of action at brainstem respiratory centers. Well-established in opioid pharmacology literature (Stubhaug 2012).

hepatic Hepatic impairmenttracerelativerelativemedium
Editorial

Codeine is extensively hepatically metabolized (Ashraf et al. 2024). Standard pharmacological reasoning for prodrugs with hepatic metabolism.

Reasoning

Codeine is extensively hepatically metabolized (Ashraf et al. 2024). Standard pharmacological reasoning for prodrugs with hepatic metabolism.

renal Renal impairmenttracerelativerelativehigh
Editorial

Standard opioid pharmacokinetic reasoning. Codeine and metabolites are primarily renally excreted (Dahan et al. 2014). M6G accumulation in renal impairment is well-established in opioid pharmacology.

Reasoning

Standard opioid pharmacokinetic reasoning. Codeine and metabolites are primarily renally excreted (Dahan et al. 2014). M6G accumulation in renal impairment is well-established in opioid pharmacology.

Timeline Phases

oral

FieldPublishedAI ProposedConfidence
Onsettrace1800–2700 sec(i=0.05)1800–2700 sec(i=0.05)medium
Editorial

Timeline derived from PK data (Tmax 1.0\u20131.4 h, t\u00bd ~2.8 h; Mohammed et al. 1993) and community duration reports (onset 30\u201345 min, peak 3\u20135 h, total 3\u20136 h). Phase durations anchored to community ranges with PK data as corroboration. Afterglow extended to account for M6G metabolite contribution in extensive metabolizers.

Reasoning

Timeline derived from PK data (Tmax 1.0\u20131.4 h, t\u00bd ~2.8 h; Mohammed et al. 1993) and community duration reports (onset 30\u201345 min, peak 3\u20135 h, total 3\u20136 h). Phase durations anchored to community ranges with PK data as corroboration. Afterglow extended to account for M6G metabolite contribution in extensive metabolizers.

Come uptrace3600–7200 sec(i=0.30)3600–7200 sec(i=0.30)medium
Editorial

Timeline derived from PK data (Tmax 1.0\u20131.4 h, t\u00bd ~2.8 h; Mohammed et al. 1993) and community duration reports (onset 30\u201345 min, peak 3\u20135 h, total 3\u20136 h). Phase durations anchored to community ranges with PK data as corroboration. Afterglow extended to account for M6G metabolite contribution in extensive metabolizers.

Reasoning

Timeline derived from PK data (Tmax 1.0\u20131.4 h, t\u00bd ~2.8 h; Mohammed et al. 1993) and community duration reports (onset 30\u201345 min, peak 3\u20135 h, total 3\u20136 h). Phase durations anchored to community ranges with PK data as corroboration. Afterglow extended to account for M6G metabolite contribution in extensive metabolizers.

Peaktrace10800–18000 sec(i=1.00)10800–18000 sec(i=1.00)medium
Editorial

Timeline derived from PK data (Tmax 1.0\u20131.4 h, t\u00bd ~2.8 h; Mohammed et al. 1993) and community duration reports (onset 30\u201345 min, peak 3\u20135 h, total 3\u20136 h). Phase durations anchored to community ranges with PK data as corroboration. Afterglow extended to account for M6G metabolite contribution in extensive metabolizers.

Reasoning

Timeline derived from PK data (Tmax 1.0\u20131.4 h, t\u00bd ~2.8 h; Mohammed et al. 1993) and community duration reports (onset 30\u201345 min, peak 3\u20135 h, total 3\u20136 h). Phase durations anchored to community ranges with PK data as corroboration. Afterglow extended to account for M6G metabolite contribution in extensive metabolizers.

Resolutiontrace7200–14400 sec(i=0.20)7200–14400 sec(i=0.20)medium
Editorial

Timeline derived from PK data (Tmax 1.0\u20131.4 h, t\u00bd ~2.8 h; Mohammed et al. 1993) and community duration reports (onset 30\u201345 min, peak 3\u20135 h, total 3\u20136 h). Phase durations anchored to community ranges with PK data as corroboration. Afterglow extended to account for M6G metabolite contribution in extensive metabolizers.

Reasoning

Timeline derived from PK data (Tmax 1.0\u20131.4 h, t\u00bd ~2.8 h; Mohammed et al. 1993) and community duration reports (onset 30\u201345 min, peak 3\u20135 h, total 3\u20136 h). Phase durations anchored to community ranges with PK data as corroboration. Afterglow extended to account for M6G metabolite contribution in extensive metabolizers.

Afterglowtrace7200–14400 sec(i=0.05)7200–14400 sec(i=0.05)medium
Editorial

Timeline derived from PK data (Tmax 1.0\u20131.4 h, t\u00bd ~2.8 h; Mohammed et al. 1993) and community duration reports (onset 30\u201345 min, peak 3\u20135 h, total 3\u20136 h). Phase durations anchored to community ranges with PK data as corroboration. Afterglow extended to account for M6G metabolite contribution in extensive metabolizers.

Reasoning

Timeline derived from PK data (Tmax 1.0\u20131.4 h, t\u00bd ~2.8 h; Mohammed et al. 1993) and community duration reports (onset 30\u201345 min, peak 3\u20135 h, total 3\u20136 h). Phase durations anchored to community ranges with PK data as corroboration. Afterglow extended to account for M6G metabolite contribution in extensive metabolizers.

Dose Tier Summaries

thresholdtrace
medium

At threshold doses (~15 mg oral), effects are subtle and easily attributed to placebo. A mild sense of relaxation or slight warmth may be noticed, with minimal cognitive alteration. Pain perception may be marginally reduced, though the effect is unlikely to meet clinical significance in most individuals. Physically, slight pupil constriction (miosis) may be detectable. Gastrointestinal motility may slow marginally. Most individuals — particularly CYP2D6 poor metabolizers — will notice little to no subjective effect at this dose.

Editorial

Threshold dose inferred from community consensus and clinical dose-response data. Codeine's prodrug nature means threshold effects depend heavily on CYP2D6 phenotype. 15 mg produces minimal morphine (~1.5 mg equivalent) in extensive metabolizers.

Reasoning

Threshold dose inferred from community consensus and clinical dose-response data. Codeine's prodrug nature means threshold effects depend heavily on CYP2D6 phenotype. 15 mg produces minimal morphine (~1.5 mg equivalent) in extensive metabolizers.

Evidence basis: community_consensus_large

lighttrace
medium

At light doses (30–60 mg oral), mild analgesia becomes perceptible alongside gentle sedation and anxiolysis. A sense of warmth and physical comfort emerges, with mild cognitive slowing and thought deceleration. Mood elevation is subtle — a quiet contentment rather than pronounced euphoria. Mild pupil constriction, slight constipation, and occasional nausea are common physical effects. Some individuals experience mild itching (histamine-mediated). Functional impairment is minimal; most activities remain manageable though reaction time may be slightly reduced.

Editorial

30–60 mg is the standard clinical dose range for mild-to-moderate pain. Effects well-characterized in clinical literature. Subjective effects reflect modest morphine conversion (~3–6 mg morphine equivalent in extensive metabolizers).

Reasoning

30–60 mg is the standard clinical dose range for mild-to-moderate pain. Effects well-characterized in clinical literature. Subjective effects reflect modest morphine conversion (~3–6 mg morphine equivalent in extensive metabolizers).

Evidence basis: community_consensus_large

commontrace
medium

At common doses (60–120 mg oral), the characteristic opioid experience becomes clear: meaningful analgesia, sedation, and a pervasive sense of physical warmth and comfort. Anxiety suppression is pronounced. Cognitive euphoria manifests as a sense of well-being and contentment, while thought deceleration slows internal dialogue. Physically, pupil constriction is obvious, constipation is reliable, and nausea may intensify — particularly in opioid-naive individuals. Itching, especially facial or nasal, is common. Respiratory rate decreases modestly. Sexual arousal suppression and appetite suppression are typical. Functional impairment is moderate. Drowsiness may interfere with tasks requiring sustained attention. Duration is 3–5 hours of primary effects with possible residual sedation extending further.

Editorial

60–120 mg represents 1–2× the standard therapeutic dose. Effects well-established in clinical pharmacology and community reports. Morphine conversion yields ~6–12 mg morphine equivalent in extensive metabolizers.

Reasoning

60–120 mg represents 1–2× the standard therapeutic dose. Effects well-established in clinical pharmacology and community reports. Morphine conversion yields ~6–12 mg morphine equivalent in extensive metabolizers.

Evidence basis: community_consensus_large

strongtrace
medium

At strong doses (120–200 mg oral), opioid effects intensify substantially: pronounced sedation with strong tactile euphoria and marked cognitive euphoria. A heavy, enveloping warmth dominates the physical experience. Pain suppression is near-complete for mild-to-moderate pain. Thought deceleration is prominent and internal monologue may become sparse. Respiratory depression becomes clinically significant at this range, particularly in CYP2D6 extensive and ultrarapid metabolizers. Nausea and vomiting risk increases. Constipation is pronounced. Nodding — involuntary oscillation between wakefulness and drowsiness — may occur. Compulsive redosing urge may emerge. This dose range carries meaningful overdose risk, especially in opioid-naive individuals or those with uncharacterized CYP2D6 status.

Editorial

120–200 mg exceeds standard therapeutic dosing (max recommended single dose 60 mg). Effects inferred from equianalgesic conversion (~12–20 mg oral morphine equivalent) and community reports. Respiratory depression risk becomes clinically relevant.

Reasoning

120–200 mg exceeds standard therapeutic dosing (max recommended single dose 60 mg). Effects inferred from equianalgesic conversion (~12–20 mg oral morphine equivalent) and community reports. Respiratory depression risk becomes clinically relevant.

Evidence basis: community_consensus_large

heavytrace
medium

At heavy doses (>200 mg oral), the experience is dominated by profound sedation, near-unconsciousness, and severe respiratory depression. Euphoria may be intense but is often obscured by overwhelming drowsiness. Communication becomes difficult and cognitive function is markedly impaired. Respiratory depression is the primary acute danger — potentially fatal, especially in CYP2D6 ultrarapid metabolizers where morphine production may be several-fold higher than predicted. Severe nausea and vomiting, urinary retention, and significant hypotension may occur. This dose range approaches forensic toxicity thresholds. This dose range is associated with overdose fatalities. Naloxone availability and the presence of a sober companion are critical harm reduction measures at any supratherapeutic dose.

Editorial

Doses >200 mg are well above therapeutic range and approach forensic toxicity thresholds (blood concentration 0.3 mg/L). Effects extrapolated from equianalgesic morphine doses (>20 mg oral morphine equivalent) and forensic case data.

Reasoning

Doses >200 mg are well above therapeutic range and approach forensic toxicity thresholds (blood concentration 0.3 mg/L). Effects extrapolated from equianalgesic morphine doses (>20 mg oral morphine equivalent) and forensic case data.

Evidence basis: community_consensus_large

02

History

current version
published Jun 4, 2026AI-generated—
versions
1 total
publication ledger

backfill Jun 4, 2026

Historical versions do not record which reviewer approved them; editorial accountability is recorded per value in the database and in the publication ledger going forward.

full version history suggest a correctioncontact@psychedex.org
03

Sources

4 strong · 30 moderate · 6 weak
  1. [1]
    moderate
    Codeine and its alternates for pain and cough relief. I. Codeine, exclusive of its antitussive action
    Eddy NB, Friebel H, Hahn KJ, Halbach H · 1968 · Bulletin of the World Health Organization
    pubmed 49729389 claims checked5 verified4 inconclusive
  2. [2]
    moderate
    A look inside the association codeine-paracetamol: clinical pharmacology supports analgesic efficacy
    Mattia C, Coluzzi F · 2015 · European Review for Medical and Pharmacological Sciences
    pubmed 257207265 claims checked2 verified1 partial2 inconclusive
  3. [3]
    moderate
    Uniform assessment and ranking of opioid mu receptor binding constants for selected opioid drugs
    Volpe DA, McMahon Tobin GA, Mellon RD, et al. · 2011 · Regulatory Toxicology and Pharmacology
    doi.org/10.1016/j.yrtph.2010.12.007pubmed 212157852 claims checked2 verified
  4. [4]
    weak
    Pierre Jean Robiquet - Wikipedia
    Wikipedia contributors · 2024
    linkno claims checked
  5. [5]
    weak
    More codeine fatalities after tonsillectomy in North American children
    Kelly LE, Rieder M, van den Anker J, et al. · 2012 · Pediatrics
    doi.org/10.1542/peds.2011-2538pubmed 224927616 claims checked5 verified1 partial
  6. [6]
    moderate
    Changes in sales of analgesics to pharmacies after codeine was rescheduled as a prescription only medicine
    Schaffer AL, Cairns R, Brown JA, et al. · 2020 · Medical Journal of Australia
    doi.org/10.5694/mja2.50552pubmed 322005662 claims checked1 verified1 partial
  7. [7]
    moderate
    Investigation of morphine and morphine glucuronide levels and cytochrome P450 isoenzyme 2D6 genotype in codeine-related deaths
    Frost J, Helland A, Nordrum IS, Slordal L · 2012 · Forensic Science International
    doi.org/10.1016/j.forsciint.2012.01.019pubmed 222855043 claims checked2 verified1 inconclusive
  8. [8]
    moderate
    CYP2D6 genotyping in a Korean cohort: comparative analysis with Asian, Caucasian, and African populations
    Kim TD, Kwak JS, Shin JG, et al. · 2025 · Pharmacogenomics
    doi.org/10.1080/14622416.2025.2565993pubmed 410035403 claims checked1 verified2 inconclusive
  9. [9]
    strong
    Does cytochrome 2D6 genotype affect the analgesic efficacy of codeine after ambulatory surgery? Prospective trial in 987 adults
    Poikola S, von Plato H, Harju J, et al. · 2025 · Acta Anaesthesiologica Scandinavica
    doi.org/10.1111/aas.14549pubmed 395426912 claims checked2 verified
  10. [10]
    moderate
    Codeine disposition in sickle cell patients compared with healthy volunteers
    Mohammed SS, Ayass M, Mehta P, et al. · 1993 · Journal of Clinical Pharmacology
    pubmed 82274775 claims checked5 verified
  11. [11]
    moderate
    Mu receptor binding of some commonly used opioids and their metabolites
    Chen ZR, Irvine RJ, Somogyi AA, Bochner F · 1991 · Life Sciences
    pubmed 18519214 claims checked4 inconclusive
  12. [12]
    moderate
    Dental opioid prescribing rates after the up-scheduling of codeine in Australia
    Teoh L, Hollingworth S, Marino R, et al. · 2020 · Scientific Reports
    doi.org/10.1038/s41598-020-65390-6pubmed 324399501 claim checked1 verified
  13. [13]
    moderate
    PURPLE DRANK: AN OLD PHENOMENON RETURNS
    Juli R, Juli G, Juli A, Juli L · 2025 · Psychiatria Danubina
    pubmed 409828251 claim checked1 verified
  14. [14]
    moderate
    Use of 'Lean' Among Electronic Dance Music Party Attendees
    Palamar JJ · 2019 · The American Journal on Addictions
    doi.org/10.1111/ajad.12897pubmed 31041819no claims checked
  15. [15]
    moderate
    Beyond the 'purple drank': Study of promethazine abuse according to the European Medicines Agency adverse drug reaction reports
    Chiappini S, Schifano F, Corkery J, Guirguis A · 2021 · Journal of Psychopharmacology
    doi.org/10.1177/0269881120959615pubmed 334270172 claims checked2 verified
  16. [16]
    moderate
    Tyrosine aminotransferase contributes to benzylisoquinoline alkaloid biosynthesis in opium poppy
    Lee EJ, Facchini PJ · 2011 · Plant Physiology
    doi.org/10.1104/pp.111.185512pubmed 219492092 claims checked1 partial1 inconclusive
  17. [17]
    moderate
    The Implausibility of Neonatal Opioid Toxicity from Breastfeeding
    Zipursky J, Juurlink DN · 2020 · Clinical Pharmacology and Therapeutics
    doi.org/10.1002/cpt.1882pubmed 323787494 claims checked3 verified1 inconclusive
  18. [18]
    moderate
    Implementation of a Pediatric Posttonsillectomy Pain Protocol in a Large Group Practice
    Luk LJ, Mosen D, MacArthur CJ, Grosz AH · 2016 · Otolaryngology - Head and Neck Surgery
    doi.org/10.1177/0194599815627810pubmed 268843623 claims checked3 verified
  19. [19]
    moderate
    Biowaiver monographs for immediate-release solid oral dosage forms: codeine phosphate
    Dahan A, Wolk O, Zur M, et al. · 2014 · Journal of Pharmaceutical Sciences
    doi.org/10.1002/jps.23977pubmed 247882393 claims checked2 verified1 inconclusive
  20. [20]
    weak
    Codeine physical properties (CAS 76-57-3)
    ChemicalBook / INCHEM · 2024
    linkno claims checked
  21. [21]
    moderate
    Intra-Arterial, but Not Intrathecal, Baclofen and Codeine Attenuates Cough in the Cat
    Olsen WL, Rose M, Golder FJ, et al. · 2021 · Frontiers in Physiology
    doi.org/10.3389/fphys.2021.640682pubmed 337467782 claims checked2 verified
  22. [22]
    moderate
    Naloxone blocks suppression of cough by codeine in anesthetized rabbits
    Simera M, Veternik M, Poliacek I · 2013 · Advances in Experimental Medicine and Biology
    doi.org/10.1007/978-94-007-4549-0_9pubmed 228366204 claims checked4 verified
  23. [23]
    moderate
    Opioids, Opioid Antagonists (general review)
    Stubhaug A · 2012 · Scandinavian Journal of Pain
    doi.org/10.1016/j.sjpain.2016.02.003pubmed 316432002 claims checked1 verified1 inconclusive
  24. [24]
    weak
    Codeine (Wikipedia)
    Wikipedia contributors · 2024
    linkno claims checked
  25. [25]
    moderate
    Population Pharmacokinetic Quantification of CYP2D6 Activity in Codeine Metabolism in Ambulatory Surgical Patients for Model-Informed Precision Dosing
    Ashraf MW, Poikola S, Neuvonen M, et al. · 2024 · Clinical Pharmacokinetics
    doi.org/10.1007/s40262-024-01433-9pubmed 394415064 claims checked3 verified1 inconclusive
  26. [26]
    moderate
    Affinities of dihydrocodeine and its metabolites to opioid receptors
    Schmidt H, Vormfelde Sv, Klinder K, et al. · 2002 · Pharmacology & Toxicology
    pubmed 124207932 claims checked2 verified
  27. [27]
    moderate
    Design, chemical synthesis, and biological evaluation of thiosaccharide analogues of morphine- and codeine-6-glucuronide
    MacDougall JM, Zhang XD, Polgar WE, et al. · 2004 · Journal of Medicinal Chemistry
    pubmed 155091803 claims checked3 inconclusive
  28. [28]
    moderate
    A validated method for simultaneous determination of codeine, codeine-6-glucuronide, norcodeine, morphine, morphine-3-glucuronide and morphine-6-glucuronide in post-mortem blood, vitreous fluid, muscle, fat and brain tissue by LC-MS
    Frost J, Lokken TN, Brede WR, et al. · 2015 · Journal of Analytical Toxicology
    doi.org/10.1093/jat/bku145pubmed 255563732 claims checked2 verified
  29. [29]
    moderate
    CYP2D6 phenotypes are associated with adverse outcomes related to opioid medications
    St Sauver JL, Olson JE, Roger VL, et al. · 2017 · Pharmacogenomics and Personalized Medicine
    doi.org/10.2147/pgpm.s136341pubmed 287695822 claims checked2 verified
  30. [30]
    strong
    Analgesic effect of oral ibuprofen 400, 600, and 800 mg; paracetamol 500 and 1000 mg; and paracetamol 1000 mg plus 60 mg codeine in acute postoperative pain: single-dose, randomized, placebo-controlled, double-blind study
    Lyngstad G, Skjelbred P, Swanson DM, Skoglund LA · 2021 · European Journal of Clinical Pharmacology
    doi.org/10.1007/s00228-021-03231-9pubmed 346553161 claim checked1 verified
  31. [31]
    strong
    Analgesic efficacy and adverse effects of paracetamol-codeine combination in third molar surgery: a meta-analytic systematic review
    Rosa A, Miranda M, Barnaba P, et al. · 2026 · Minerva Dental and Oral Science
    doi.org/10.23736/s2724-6329.25.05216-7pubmed 417666371 claim checked1 verified
  32. [32]
    weak
    A Fatal Case Report Resulting from the Abuse of the Designer Benzodiazepines Clonazolam and Flualprazolam in Conjunction with Dried Opium Poppy Pods
    Theofel N, Möller P, Vejmelka E, Kramer C, Tsokos M, Scholtis S · 2023 · Journal of Analytical Toxicology
    doi.org/10.1093/jat/bkac098pubmed 365162361 claim checked1 verified
  33. [33]
    moderate
    Practice implications and recommendations for managing codeine misuse and dependence
    Bergin M, Norman I, Foley M, et al. · 2015 · Acta Pharmaceutica
    doi.org/10.1515/acph-2015-0040pubmed 266778941 claim checked1 inconclusive
  34. [34]
    moderate
    Purchasing Over The Counter (OTC) Medicinal Products Containing Codeine - Easy Access, Advertising, Misuse and Perceptions of Medicinal Risk
    Wells JS, Bergin M, Van Hout MC, et al. · 2018 · Journal of Pharmacy & Pharmaceutical Sciences
    doi.org/10.18433/jpps30049pubmed 300112591 claim checked1 verified
  35. [35]
    moderate
    Pharmacists' experience with patients suspected to be addicted to over-the-counter codeine and their attitudes towards potential remediation strategies
    Margan Koletic Z, Pavlicic B, et al. · 2025 · BMC Psychiatry
    doi.org/10.1186/s12888-025-06881-6pubmed 403077771 claim checked1 verified
  36. [36]
    strong
    A mixed-methods systematic review of the prevalence, reasons, associated harms and risk-reduction interventions of OTC medicines misuse, abuse and dependence in adults
    Algarni M, Hadi MA, Yahyouche A, et al. · 2021 · Journal of Pharmaceutical Policy and Practice
    doi.org/10.1186/s40545-021-00350-7pubmed 345179253 claims checked1 partial2 inconclusive
  37. [37]
    weak
    Detoxification from high-dose codeine dependence: induction onto and tapering of buprenorphine in an inpatient addiction unit
    Teixeira FM, Krzanowski J, Ilves L, Archer JR · 2025 · BMJ Case Reports
    doi.org/10.1136/bcr-2025-268674pubmed 411734831 claim checked1 verified
  38. [38]
    moderate
    Evaluation of poly-drug use in methadone-related fatalities using segmental hair analysis
    Nielsen MK, Johansen SS, Linnet K · 2015 · Forensic Science International
    doi.org/10.1016/j.forsciint.2015.01.004pubmed 256220322 claims checked2 verified
  39. [39]
    moderate
    Serotonin syndrome and pain medication: What is relevant for practice?
    Schenk M, Wirz S · 2015 · Schmerz
    doi.org/10.1007/s00482-015-1512-0pubmed 258602003 claims checked1 verified2 inconclusive
  40. [40]
    moderate
    'Weak' opioid analgesics. Codeine, dihydrocodeine and tramadol: no less risky than morphine
    Prescrire International · 2016 · Prescrire International
    pubmed 270427323 claims checked1 verified2 inconclusive
04

Claim Verification

Citation-bearing claims in this article were checked by an AI model against the abstract of the source they cite — every safety-critical claim, plus a sample of the rest. Verdicts below are model-issued, not human-issued; when an editor overrides a verdict, the override is recorded alongside it. Claims whose source does not support them are flagged for editorial review.

summary12 claims5verified2partial5inconclusive
verifiedOral duration is 3–6 hours, with an elimination half-life of approximately 2.8 hours.[10]model confidence 92%
Verified

The abstract directly confirms t1/2 2.8h in healthy volunteers. Oral duration of 3–6 hours is not explicitly stated but is a reasonable clinical inference from PK parameters; the key cited fact (half-life) is confirmed.

After 60mg oral codeine: Tmax 1.4h (healthy), Cmax 225 ng/mL, t1/2 2.8h, plasma protein binding ~30%. High hepatic extraction drug.

checked by claude-sonnet-4-6 · Apr 24, 2026

partialFatal pediatric cases in CYP2D6 ultrarapid metabolizers prompted an FDA black box warning in 2013, and Australia rescheduled codeine to prescription-only in 2018[5]model confidence 82%
Partial

The abstract confirms the CYP2D6-related pediatric fatalities that underpinned the FDA warning, but does not mention the FDA black box warning in 2013 or the Australia 2018 rescheduling. The compound claim is only half-supported by this citation.

3 additional fatal or life-threatening codeine cases in children post-adenotonsillectomy; CYP2D6 functional gene duplications caused excessive morphine production.

checked by claude-sonnet-4-6 · Apr 24, 2026

partialFatal pediatric cases in CYP2D6 ultrarapid metabolizers prompted an FDA black box warning in 2013, and Australia rescheduled codeine to prescription-only in 2018[6]model confidence 82%
Partial

The abstract confirms the Australia 2018 prescription-only rescheduling, but does not mention the FDA black box warning in 2013 or the CYP2D6 pediatric fatalities. The compound claim is only half-supported by this citation.

Australia rescheduled codeine to prescription-only in February 2018. Followed by increased sales of paracetamol, ibuprofen, and combination products.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedThe largest prospective trial examining CYP2D6 genotype and codeine analgesia (987 adults) was published in 2025.[9]model confidence 85%
Verified

The abstract confirms the 987-patient prospective trial investigating CYP2D6 genotype effect on codeine analgesia. Publication year 2025 is not mentioned in the abstract but is not contradicted; the described paper matches all other characteristics.

987-patient prospective trial of paracetamol-codeine after day surgery; investigates CYP2D6 genotype effect on analgesic efficacy and adverse effects.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCodeine binds weakly to mu-opioid receptors (Ki >100 nM at human MOR, approximately 100–250× lower affinity than morphine at Ki ~1.2 nM)[3]model confidence 93%
Verified

The abstract directly confirms codeine Ki > 100 nM at recombinant human MOR. The morphine Ki comparison (~1.2 nM, 100–250× difference) is not in this abstract but is supported by other cited sources; the key claimed value is confirmed here.

Experiments to obtain Ki values for 19 approved opioid drugs using a single binding assay in a cell membrane preparation expressing recombinant human MOR. Codeine Ki > 100 nM.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveCodeine binds weakly to mu-opioid receptors (Ki >100 nM at human MOR, approximately 100–250× lower affinity than morphine at Ki ~1.2 nM)[11]model confidence 70%
Inconclusive

The abstract confirms qualitatively weak mu receptor binding and that the methoxy group reduces affinity, but provides no specific Ki values for codeine or morphine to verify the numerical assertions (Ki >100 nM, ~1.2 nM, 100–250× difference).

Codeine has relatively weak mu receptor binding; metabolite morphine-6-glucuronide is much more potent. Methoxy group at position 3 reduces binding.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveApproximately 10% of an oral dose undergoes CYP2D6 O-demethylation to morphine; the remainder follows CYP3A4 N-demethylation to inactive norcodeine (~10%) or UGT2B7 glucuronidation to codeine-6-glucuronide (~70–80%).[1]model confidence 75%
Inconclusive

This WHO review abstract covers general pharmacology and toxicity comparisons with morphine, but makes no mention of CYP2D6, CYP3A4, UGT2B7, or the specific metabolic pathway percentages claimed. The data would need to be in the full text.

Comprehensive WHO review of codeine analgesia, pharmacology, side effects, toxicity. Codeine more toxic to animals (convulsant) but less toxic to man than morphine (less respiratory depression). Tolerance and dependence less frequent than morphine; less intense abstinence syndrome.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveApproximately 10% of an oral dose undergoes CYP2D6 O-demethylation to morphine; the remainder follows CYP3A4 N-demethylation to inactive norcodeine (~10%) or UGT2B7 glucuronidation to codeine-6-glucuronide (~70–80%).[2]model confidence 72%
Inconclusive

The abstract confirms CYP2D6 variability and mentions norcodeine and C6G as metabolites, but does not provide the specific pathway percentages (~10% morphine, ~10% norcodeine, ~70–80% C6G) or identify the specific enzymes CYP3A4 and UGT2B7.

Codeine activity is not only via morphine conversion but also by codeine itself and metabolites norcodeine and codeine-6-glucuronide.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveEuphoria intensity correlates directly with CYP2D6 metabolizer status — poor metabolizers experience negligible mood effects while ultrarapid metabolizers may experience disproportionate euphoria and respiratory depression[1]model confidence 80%
Inconclusive

The WHO review abstract addresses general pharmacology and toxicity but does not mention CYP2D6, metabolizer status, euphoria, or mood effects. The specific claim about genotype-dependent euphoria cannot be verified from this abstract.

Comprehensive WHO review of codeine analgesia, pharmacology, side effects, toxicity. Codeine more toxic to animals (convulsant) but less toxic to man than morphine (less respiratory depression).

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedAcute overdose risk is moderate: forensic toxicology thresholds place toxicity at blood concentrations of 0.3 mg/L and potentially lethal concentrations at 1.6 mg/L[7]model confidence 97%
Verified

The abstract directly confirms both thresholds: TIAFT toxicity threshold 0.3 mg/L and lethal threshold 1.6 mg/L in postmortem blood.

TIAFT toxicity threshold 0.3 mg/L; lethal threshold 1.6 mg/L.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveCYP2D6 ultrarapid metabolizer status transforms standard therapeutic doses into potentially fatal exposures — a risk affecting up to 18% of some Latin American and African populations[8]model confidence 72%
Inconclusive

The abstract confirms CYP2D6 is highly polymorphic with interethnic variation, but does not provide the specific 18% prevalence figure for Latin American or African populations. The specific number cannot be verified from the abstract alone.

CYP2D6 is highly polymorphic with interindividual and interethnic variation. Metabolizes ~20% of prescribed drugs.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedPhysical and psychological dependence are moderate, developing through mu-opioid receptor downregulation with repeated use; withdrawal is milder and shorter than morphine withdrawal[1]model confidence 85%
Verified

The abstract confirms that dependence is less frequent and the abstinence syndrome is less intense than morphine, supporting 'milder and shorter' withdrawal. The molecular mechanism (mu-opioid receptor downregulation) is not in the abstract but is standard pharmacology not contradicted here.

Tolerance and dependence less frequent than morphine; less intense abstinence syndrome.

checked by claude-sonnet-4-6 · Apr 24, 2026

history8 claims7verified1partial
verified2012: Kelly et al. reported three fatal or life-threatening cases in North American children following adenotonsillectomy, linked to CYP2D6 ultrarapid metabolizer status with gene duplications.[5]model confidence 93%
Verified

The abstract confirms all key factual elements: 3 fatal or life-threatening cases in children post-adenotonsillectomy, with CYP2D6 functional gene duplications causing excessive morphine production. Author name and year are not in the abstract but are consistent with the paper title and scope.

3 additional fatal or life-threatening codeine cases in children post-adenotonsillectomy; CYP2D6 functional gene duplications caused excessive morphine production.

checked by claude-sonnet-4-6 · Apr 24, 2026

verified2018 (February 1): Australia rescheduled codeine from over-the-counter (Schedule 3, pharmacist-only) to prescription-only, citing dependence and misuse concerns. The rescheduling was followed by measurable shifts in analgesic sales patterns.[6]model confidence 92%
Verified

The abstract confirms prescription-only rescheduling in February 2018 and measurable analgesic sales shifts post-rescheduling. Specific reasons cited and 'Schedule 3' designation not mentioned but core facts confirmed.

Australia rescheduled codeine to prescription-only in February 2018. Followed by increased sales of paracetamol, ibuprofen, and combination products.

checked by claude-sonnet-4-6 · Apr 24, 2026

verified2018 (February 1): Australia rescheduled codeine from over-the-counter (Schedule 3, pharmacist-only) to prescription-only, citing dependence and misuse concerns. The rescheduling was followed by measurable shifts in analgesic sales patterns.[12]model confidence 93%
Verified

The abstract directly confirms February 1, 2018 as the rescheduling date and documents measurable prescribing behavior changes post-rescheduling (increased dental opioid prescribing).

Australia codeine rescheduled to prescription-only February 1, 2018. Opioid prescribing in dentistry increased significantly post-rescheduling.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedPromethazine abuse in this context is independently associated with drug-related fatalities.[15]model confidence 94%
Verified

The abstract directly confirms promethazine is often co-abused with codeine in 'purple drank' and is associated with drug-related fatalities.

EMA data on promethazine misuse; often co-abused with opioids (codeine) in 'purple drank' preparations. Associated with drug-related fatalities.

checked by claude-sonnet-4-6 · Apr 24, 2026

partialCodeine constitutes approximately 2% of opium by weight and is biosynthesized in the poppy plant via the benzylisoquinoline alkaloid pathway from tyrosine precursors[16]model confidence 80%
Partial

The abstract confirms codeine is a BIA from Papaver somniferum biosynthesized via the benzylisoquinoline alkaloid pathway with tyrosine aminotransferase as an enzyme, supporting the pathway claim. However, '~2% of opium by weight' is not mentioned in the abstract.

Codeine, morphine, and noscapine are pharmaceutical BIAs from Papaver somniferum. TyrAT is an enzyme in the biosynthetic pathway for these alkaloids.

checked by claude-sonnet-4-6 · Apr 24, 2026

verified2009: The first reported neonatal death attributed to maternal codeine use during breastfeeding — the "Toronto case" — drew international attention. Subsequent critical reanalysis by Zipursky and Juurlink argued the causal link is implausible, citing the small quantities of opioids transferred through breast milk regardless of CYP2D6 genotype and the absence of other confirmed neonatal deaths despite widespread codeine use among breastfeeding mothers.[17]model confidence 88%
Verified

The abstract confirms the reexamination of the Toronto case and the conclusion that the causal link is implausible. The specific arguments cited (breast milk quantities, absence of other deaths) are not in the abstract but the paper is confirmed to argue implausibility. The 2009 date is not in the abstract.

Reexamines the 'Toronto case' of infant death linked to maternal codeine/CYP2D6 ultrarapid metabolizer status. Argues the causal link is implausible.

checked by claude-sonnet-4-6 · Apr 24, 2026

verified2016: Kaiser Permanente implemented an electronic health record protocol restricting codeine prescribing for children under 7 years.[18]model confidence 90%
Verified

The abstract confirms Kaiser Permanente implemented an EHR-based protocol restricting codeine for children under 7. The year 2016 is not in the abstract but all other facts are confirmed.

Kaiser Permanente restricted codeine for children <7 years old following respiratory failure and death cases. EHR-based protocol compliance study.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedThe recreational preparation known as "purple drank" (also "lean" or "sizzurp") — codeine-promethazine cough syrup mixed with soft drinks and sometimes candy — originated in the Houston, Texas music scene in the 1960s and gained widespread popularity through hip-hop culture in the 1990s and 2000s[13]model confidence 95%
Verified

The abstract confirms purple drank (codeine + promethazine + soda) originated in Texas in the 1960s and became widespread in the 1990s.

Purple drank (codeine + promethazine + soda/alcohol). Used in Texas 1960s; widespread in 1990s.

checked by claude-sonnet-4-6 · Apr 24, 2026

chemistry2 claims2inconclusive
inconclusive<div class="compact-kv"> <table> <tbody> <tr><td>Melting point</td><td>154–158 °C (free base)</td></tr> <tr><td>Density</td><td>1.32 g/cm³ at 25 °C</td></tr> <tr><td>Water solubility</td><td>Slightly soluble (1:120 w/v); very soluble in dilute acids</td></tr> <tr><td>Organic solubility</td><td>1:2 in alcohol, 1:0.5 in chloroform, 1:50 in ether</td></tr> <tr><td>BCS classification</td><td>Class I (high solubility, high permeability)</td></tr> </tbody> </table> </div>[19]model confidence 70%
Inconclusive

The abstract confirms BCS Class I designation and high solubility criteria. However, the specific physical chemistry values (melting point 154–158°C, density 1.32 g/cm³, specific organic solubility ratios) are not mentioned and would require the full monograph text to verify.

Codeine fraction absorbed >90% orally. Meets 'highly soluble' criteria. CYP2D6 polymorphism cited as primary toxicity risk. Class 1 BCS drug.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveIt is biosynthesized via the benzylisoquinoline alkaloid pathway: tyrosine → dopamine + 4-hydroxyphenylacetaldehyde → (S)-norcoclaurine → (S)-reticuline → salutaridine → thebaine → codeine → morphine[16]model confidence 72%
Inconclusive

The abstract confirms TyrAT (tyrosine aminotransferase) is involved in BIA biosynthesis in Papaver somniferum, but does not enumerate the specific intermediate steps (norcoclaurine, reticuline, salutaridine, thebaine) in the pathway. These would require full text.

Codeine, morphine, and noscapine are pharmaceutical BIAs from Papaver somniferum. TyrAT is an enzyme in the biosynthetic pathway for these alkaloids.

checked by claude-sonnet-4-6 · Apr 24, 2026

pharmacology13 claims9verified1partial3inconclusive
verifiedIts direct affinity for opioid receptors is weak (Ki >100 nM at human mu-opioid receptor; Ki ~0.3 µmol/L at guinea pig cortical MOR), approximately 100–250× lower than morphine (Ki ~1.2 nM)[3]model confidence 93%
Verified

The abstract directly confirms codeine Ki > 100 nM using recombinant human MOR in a standardized binding assay across 19 opioid drugs.

Experiments to obtain Ki values for 19 approved opioid drugs using a single binding assay in a cell membrane preparation expressing recombinant human MOR. Codeine Ki > 100 nM.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedIts direct affinity for opioid receptors is weak (Ki >100 nM at human mu-opioid receptor; Ki ~0.3 µmol/L at guinea pig cortical MOR), approximately 100–250× lower than morphine (Ki ~1.2 nM)[26]model confidence 93%
Verified

The abstract directly confirms codeine Ki ~0.3 micromol/L at mu receptor, consistent with the ~0.3 µmol/L claim. This paper provides the guinea pig cortical MOR value.

Codeine Ki at mu receptor ~0.3 micromol/L; at delta receptor ~5.9 micromol/L; at kappa receptor ~14 micromol/L.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveIts direct affinity for opioid receptors is weak (Ki >100 nM at human mu-opioid receptor; Ki ~0.3 µmol/L at guinea pig cortical MOR), approximately 100–250× lower than morphine (Ki ~1.2 nM)[11]model confidence 68%
Inconclusive

The abstract confirms qualitatively weak mu receptor binding, but provides no specific Ki values to verify the numerical assertions (>100 nM, ~0.3 µmol/L, ~1.2 nM for morphine, 100–250× difference).

Codeine has relatively weak mu receptor binding; metabolite morphine-6-glucuronide is much more potent. Methoxy group at position 3 reduces binding.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveThe pharmacological activity of codeine is predominantly mediated through its active metabolite morphine, produced by hepatic CYP2D6-catalyzed O-demethylation of the 3-methoxy group.[1]model confidence 72%
Inconclusive

This WHO review abstract covers general toxicity comparisons but does not mention CYP2D6, O-demethylation, or the prodrug mechanism. The specific mechanistic claim cannot be verified from this abstract.

Comprehensive WHO review of codeine analgesia, pharmacology, side effects, toxicity. Codeine more toxic to animals (convulsant) but less toxic to man than morphine (less respiratory depression).

checked by claude-sonnet-4-6 · Apr 24, 2026

partialThe pharmacological activity of codeine is predominantly mediated through its active metabolite morphine, produced by hepatic CYP2D6-catalyzed O-demethylation of the 3-methoxy group.[2]model confidence 80%
Partial

The abstract explicitly states that codeine activity is 'not only via morphine conversion but also by codeine itself and metabolites norcodeine and codeine-6-glucuronide,' which partially contradicts the 'predominantly via morphine' framing. CYP2D6 O-demethylation is mentioned. The claim overstates morphine's exclusive role.

Codeine activity is not only via morphine conversion but also by codeine itself and metabolites norcodeine and codeine-6-glucuronide.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveUGT2B7 glucuronidation → codeine-6-glucuronide (C6G, ~70–80% of dose) — weak direct opioid activity[2]model confidence 70%
Inconclusive

The abstract mentions C6G and confirms it has some opioid activity, but does not mention UGT2B7 as the enzyme responsible or the ~70–80% dose contribution. These specific claims cannot be verified from the abstract.

Codeine activity is not only via morphine conversion but also by codeine itself and metabolites norcodeine and codeine-6-glucuronide.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCodeine itself, norcodeine, and C6G may contribute modest opioid activity independent of morphine conversion, though this contribution is pharmacologically minor at therapeutic doses.[2]model confidence 90%
Verified

The abstract directly confirms that codeine activity includes contributions from codeine itself, norcodeine, and C6G beyond morphine conversion, consistent with the claim of modest independent activity.

Codeine activity is not only via morphine conversion but also by codeine itself and metabolites norcodeine and codeine-6-glucuronide.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedIntra-arterial (brainstem) administration suppresses cough, while spinal intrathecal administration does not — localizing the antitussive site to brainstem mu-opioid receptors[21]model confidence 97%
Verified

The abstract directly confirms intra-arterial codeine suppresses cough while intrathecal does not, and localizes the effect to brainstem.

Antitussive effect of codeine is brainstem-restricted, not spinal. Intra-arterial codeine suppresses cough; intrathecal does not.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedIntra-arterial (brainstem) administration suppresses cough, while spinal intrathecal administration does not — localizing the antitussive site to brainstem mu-opioid receptors[22]model confidence 88%
Verified

The abstract confirms brainstem-restricted antitussive effect and mu-opioid mechanism. The specific intra-arterial vs intrathecal comparison is the other paper; this abstract supports brainstem localization and MOR mechanism.

Naloxone pretreatment abolishes codeine's cough-suppressive effects, confirming mu-opioid mechanism in antitussive action. Brainstem-restricted effect.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedNaloxone pretreatment completely abolishes codeine's antitussive effect, confirming the mu-opioid mechanism.[22]model confidence 97%
Verified

The abstract directly confirms naloxone abolishes codeine's cough-suppressive effects, confirming mu-opioid mechanism.

Naloxone pretreatment abolishes codeine's cough-suppressive effects, confirming mu-opioid mechanism in antitussive action.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedOpioid receptor agonism in the enteric nervous system reduces gastrointestinal motility, causing constipation and slowed intestinal transit — a peripheral opioid effect that is clinically prominent even at therapeutic doses.[23]model confidence 88%
Verified

The abstract confirms constipation and decreased GI motility as effects of opioid receptor agonism. The enteric nervous system mechanism is not specified but the GI effects are confirmed.

Effects: analgesia, euphoria, sedation, respiratory depression, constipation, decreased GI motility.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCodeine is classified as BCS Class I (high solubility, high permeability), with >90% of an oral dose absorbed from the gastrointestinal tract[19]model confidence 97%
Verified

The abstract directly confirms >90% oral absorption, 'highly soluble' criteria, and Class 1 BCS classification.

Codeine fraction absorbed >90% orally. Meets 'highly soluble' criteria. Class 1 BCS drug.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedHepatic extraction is high, with clearance approximating hepatic blood flow[10]model confidence 95%
Verified

The abstract directly characterizes codeine as a 'High hepatic extraction drug.'

High hepatic extraction drug.

checked by claude-sonnet-4-6 · Apr 24, 2026

receptor pharmacology4 claims1verified3inconclusive
inconclusiveFor comparison, morphine binds mu receptors with Ki ~1.2 nM, making codeine's direct mu affinity approximately 100–250× weaker.[11]model confidence 68%
Inconclusive

The abstract confirms codeine has weak mu receptor binding and M6G is more potent, but does not provide specific Ki values for morphine (~1.2 nM) or quantify the fold-difference. The numerical comparison cannot be verified.

Codeine has relatively weak mu receptor binding; metabolite morphine-6-glucuronide is much more potent.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveMorphine: Ki ~1.2 nM at mu-opioid receptor — the primary mediator of codeine's analgesic, euphorigenic, and respiratory depressant effects[11]model confidence 68%
Inconclusive

The abstract does not provide morphine's Ki value (~1.2 nM). It confirms codeine's weak binding and M6G's potency, but does not give morphine binding data needed to verify this claim.

Codeine has relatively weak mu receptor binding; metabolite morphine-6-glucuronide is much more potent.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveCodeine-6-glucuronide (C6G): Weak but measurable opioid activity; represents the quantitatively dominant metabolite (~70–80% of dose) but contributes modest pharmacological effect[27]model confidence 72%
Inconclusive

The abstract confirms C6G has weak opioid activity at mu, delta, and kappa receptors. However, '~70–80% of dose' is a metabolic proportion claim not addressed in this receptor binding paper.

Codeine-6-glucuronide (C6G) examined as a weak opioid active metabolite. Thiosaccharide analogues of C6G evaluated at mu, delta, and kappa opioid receptors. C6G has weaker activity than M6G.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedClassification as a "kappa-opioid receptor agonist" is unsupported by published binding data — codeine has the lowest affinity for kappa receptors (Ki ~14 µmol/L) of the three opioid receptor subtypes tested.[26]model confidence 97%
Verified

The abstract directly confirms codeine Ki at kappa receptor ~14 micromol/L, which is the lowest of the three subtypes tested (mu ~0.3, delta ~5.9, kappa ~14).

Codeine Ki at mu receptor ~0.3 micromol/L; at delta receptor ~5.9 micromol/L; at kappa receptor ~14 micromol/L.

checked by claude-sonnet-4-6 · Apr 24, 2026

neuroscience5 claims3verified2inconclusive
verifiedCodeine's antitussive action is localized to brainstem cough centers, as demonstrated by the selective efficacy of intra-arterial (but not intrathecal) codeine administration and abolition of antitussive effect by naloxone.[21]model confidence 92%
Verified

The abstract confirms brainstem restriction and the intra-arterial vs intrathecal distinction. Naloxone abolition is from the companion paper; this abstract provides the anatomical localization evidence.

Antitussive effect of codeine is brainstem-restricted, not spinal. Intra-arterial codeine suppresses cough; intrathecal does not.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCodeine's antitussive action is localized to brainstem cough centers, as demonstrated by the selective efficacy of intra-arterial (but not intrathecal) codeine administration and abolition of antitussive effect by naloxone.[22]model confidence 92%
Verified

The abstract confirms naloxone abolition of antitussive effect and brainstem restriction. The intra-arterial vs intrathecal distinction is from the companion paper.

Naloxone pretreatment abolishes codeine's cough-suppressive effects, confirming mu-opioid mechanism in antitussive action. Brainstem-restricted effect.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCodeine's antitussive action is localized to brainstem cough centers, as demonstrated by the selective efficacy of intra-arterial (but not intrathecal) codeine administration and abolition of antitussive effect by naloxone.[22]model confidence 92%
Verified

Confirmed again from the same abstract — naloxone abolition and brainstem restriction both confirmed.

Naloxone pretreatment abolishes codeine's cough-suppressive effects, confirming mu-opioid mechanism in antitussive action. Brainstem-restricted effect.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveDoes CYP2D6 genotype affect central opioid receptor occupancy independently of plasma morphine levels? Population PK modeling has quantified peripheral metabolite ratios, but whether CNS morphine exposure follows plasma predictions in all phenotype groups remains unconfirmed.[25]model confidence 72%
Inconclusive

The abstract addresses peripheral plasma PK and metabolite quantification across CYP2D6 phenotypes, but does not address CNS receptor occupancy or whether CNS morphine exposure matches plasma predictions. The CNS question is an open research question not answered by the abstract.

Codeine metabolism quantified across CYP2D6 phenotypes. CYP2D6 genotype strongly determines morphine production via O-demethylation.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveWhat is the relative contribution of codeine-6-glucuronide to clinical effect? C6G constitutes 70–80% of the dose and possesses weak opioid activity, but its CNS penetration and in vivo potency at mu-opioid receptors are poorly characterized.[27]model confidence 70%
Inconclusive

The abstract confirms C6G has weak opioid activity at mu receptors (weaker than M6G), but does not address the 70–80% dose contribution or CNS penetration. The key claims about dose proportion and CNS penetration cannot be verified from this abstract.

Codeine-6-glucuronide (C6G) examined as a weak opioid active metabolite. Thiosaccharide analogues of C6G evaluated at mu, delta, and kappa opioid receptors. C6G has weaker activity than M6G.

checked by claude-sonnet-4-6 · Apr 24, 2026

pharmacokinetic detail11 claims10verified1inconclusive
verifiedCYP2D6 phenotype is associated with adverse opioid outcomes in clinical populations[29]model confidence 97%
Verified

Directly confirmed.

CYP2D6 phenotype affects opioid response in both poor and ultrarapid metabolizers. Clinical outcomes data in primary care population.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedPeak plasma concentration (Cmax) following a 60 mg oral dose ranges from 172–225 ng/mL, achieved at a Tmax of 1.0–1.4 hours[10]model confidence 88%
Verified

The abstract confirms Cmax 225 ng/mL and Tmax 1.4h in healthy volunteers. The paper compares healthy vs sickle cell patients, so the lower bound of the range (172 ng/mL, 1.0h) likely comes from the patient group within the same paper.

After 60mg oral codeine: Tmax 1.4h (healthy), Cmax 225 ng/mL, t1/2 2.8h, plasma protein binding ~30%.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedOral codeine absorption exceeds 90%, consistent with its BCS Class I designation (high solubility, high permeability)[19]model confidence 97%
Verified

Directly confirmed: >90% oral absorption and Class 1 BCS designation.

Codeine fraction absorbed >90% orally. Meets 'highly soluble' criteria. Class 1 BCS drug.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedPlasma protein binding is low (~30%), and hepatic extraction is high, with total clearance approximating hepatic blood flow[10]model confidence 97%
Verified

The abstract directly confirms plasma protein binding ~30% and high hepatic extraction.

After 60mg oral codeine: Tmax 1.4h (healthy), Cmax 225 ng/mL, t1/2 2.8h, plasma protein binding ~30%. High hepatic extraction drug.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCodeine undergoes extensive hepatic metabolism via three principal pathways:[25]model confidence 85%
Verified

The abstract confirms codeine undergoes extensive CYP2D6-mediated hepatic metabolism. 'Three principal pathways' is not explicitly stated but is consistent with the paper's scope of metabolic quantification.

Codeine metabolism quantified across CYP2D6 phenotypes. CYP2D6 genotype strongly determines morphine production via O-demethylation.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusivePhase II — UGT2B7 glucuronidation: Codeine → codeine-6-glucuronide (C6G, ~70–80% of dose). C6G possesses weak opioid activity.[27]model confidence 72%
Inconclusive

The abstract confirms C6G has weak opioid activity but does not address UGT2B7 as the enzyme or the ~70–80% dose contribution. This is a receptor binding paper, not a metabolic pathway paper.

Codeine-6-glucuronide (C6G) examined as a weak opioid active metabolite. C6G has weaker activity than M6G.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedAn LC-MS method capable of simultaneously quantifying codeine, C6G, norcodeine, morphine, M3G, and M6G in postmortem tissues has been validated.[28]model confidence 97%
Verified

The abstract confirms the validated LC-MS method for codeine and metabolites in postmortem tissues. The paper title lists the exact analytes.

Validated forensic method for codeine and metabolite quantification in postmortem tissues. Validated range 1.5-300 ng/mL.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCYP2D6 is one of the most polymorphic human cytochrome P450 enzymes, with clinically meaningful interindividual and interethnic variability:[8]model confidence 95%
Verified

The abstract directly confirms CYP2D6 is highly polymorphic with interindividual and interethnic variation.

CYP2D6 is highly polymorphic with interindividual and interethnic variation. Metabolizes ~20% of prescribed drugs.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCYP2D6 is one of the most polymorphic human cytochrome P450 enzymes, with clinically meaningful interindividual and interethnic variability:[25]model confidence 90%
Verified

The abstract confirms CYP2D6 genotype strongly determines morphine production, consistent with clinically meaningful variability in codeine metabolism.

Codeine metabolism quantified across CYP2D6 phenotypes. CYP2D6 genotype strongly determines morphine production via O-demethylation.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedPopulation pharmacokinetic modeling quantifying CYP2D6 activity across phenotype groups in surgical patients has been conducted to support model-informed precision dosing.[25]model confidence 97%
Verified

The abstract directly describes population PK quantification of CYP2D6 across phenotypes in ambulatory surgical patients for model-informed precision dosing.

Codeine metabolism quantified across CYP2D6 phenotypes. CYP2D6 genotype strongly determines morphine production via O-demethylation.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedThe terminal elimination half-life of codeine is approximately 2.8 hours in healthy adults[10]model confidence 97%
Verified

Directly confirmed: t1/2 2.8h in healthy volunteers.

After 60mg oral codeine: Tmax 1.4h (healthy), Cmax 225 ng/mL, t1/2 2.8h.

checked by claude-sonnet-4-6 · Apr 24, 2026

clinical evidence7 claims7verified
verifiedA randomized, placebo-controlled, double-blind, single-dose trial compared paracetamol 1000 mg + codeine 60 mg against ibuprofen (400, 600, 800 mg) and paracetamol (500, 1000 mg) in acute postoperative pain[30]model confidence 97%
Verified

The abstract directly confirms the RCT design comparing paracetamol 1000mg/codeine 60mg vs ibuprofen 400/600/800mg and paracetamol alone in post-surgical pain.

Paracetamol 1000mg/codeine 60mg vs ibuprofen 400/600/800mg and paracetamol alone in post-surgical pain.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedThe number needed to treat (NNT) for at least 50% pain relief with paracetamol 1000 mg + codeine 60 mg is 2.3–3.1, indicating clinically meaningful analgesic benefit from the combination[2]model confidence 97%
Verified

The abstract directly confirms NNT reduced to 2.3–3.1 with paracetamol + codeine combination.

Addition of codeine to paracetamol reduces NNT from 5 to 2.3-3.1.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedKelly et al. (2012) documented three fatal or life-threatening cases post-adenotonsillectomy in children with CYP2D6 gene duplications.[5]model confidence 95%
Verified

The abstract confirms all key factual elements: 3 cases, post-adenotonsillectomy, children, CYP2D6 gene duplications causing excessive morphine production.

3 additional fatal or life-threatening codeine cases in children post-adenotonsillectomy; CYP2D6 functional gene duplications caused excessive morphine production.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedThe largest prospective trial to date enrolled 987 adults receiving paracetamol-codeine after ambulatory surgery to investigate the effect of CYP2D6 genotype on analgesic efficacy and adverse effects[9]model confidence 97%
Verified

Directly confirmed in the abstract.

987-patient prospective trial of paracetamol-codeine after day surgery; investigates CYP2D6 genotype effect on analgesic efficacy and adverse effects.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedThe most recent meta-analytic systematic review evaluated the analgesic efficacy and adverse effects of paracetamol-codeine combination specifically in third molar surgery[31]model confidence 95%
Verified

Directly confirmed: systematic review and meta-analysis of paracetamol + codeine for third molar surgery, assessing efficacy and adverse events.

Systematic review and meta-analysis of paracetamol + codeine for postoperative pain after third molar surgery.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedLuk et al. (2016) reported Kaiser Permanente's institutional protocol restricting codeine in children under 7 years in response to FDA safety communications.[18]model confidence 90%
Verified

The abstract confirms Kaiser Permanente restricted codeine for children under 7 following safety cases with an EHR protocol. Author name and 2016 year are not in the abstract but are consistent with the paper.

Kaiser Permanente restricted codeine for children <7 years old following respiratory failure and death cases. EHR-based protocol compliance study.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedThe Zipursky and Juurlink (2020) critical reanalysis of the landmark breastfeeding case challenged the causal attribution on pharmacological grounds.[17]model confidence 95%
Verified

The abstract confirms the paper critically reexamines the Toronto case and argues the causal link is implausible.

Reexamines the 'Toronto case' of infant death linked to maternal codeine/CYP2D6 ultrarapid metabolizer status. Argues the causal link is implausible.

checked by claude-sonnet-4-6 · Apr 24, 2026

safety30 claims19verified1partial10inconclusive
inconclusiveThe primary mechanism of acute codeine toxicity is respiratory depression, mediated by morphine (the active metabolite) acting at mu-opioid receptors in brainstem respiratory centers[7]model confidence 72%
Inconclusive

The abstract reports forensic toxicology thresholds and morphine:codeine variability data, but does not discuss the mechanism of toxicity (respiratory depression, morphine's role, brainstem receptors). The mechanistic claim cannot be verified from this abstract.

111 cases with detectable codeine in postmortem blood from 1444 autopsies. TIAFT toxicity threshold 0.3 mg/L; lethal threshold 1.6 mg/L.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedMorphine-to-codeine ratios were highly variable even when CYP2D6 genotype was known, indicating that genotype alone cannot reliably predict morphine levels in overdose.[7]model confidence 97%
Verified

The abstract directly confirms high variability in morphine:codeine ratios even with CYP2D6 genotyping.

High variability in morphine:codeine ratios even with CYP2D6 genotyping.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCodeine produces less respiratory depression than morphine at clinically equivalent analgesic doses in humans, though it is paradoxically more toxic in some animal models due to convulsant properties.[1]model confidence 97%
Verified

The abstract directly confirms: codeine more toxic to animals (convulsant) but less toxic to man than morphine, with less respiratory depression.

Codeine more toxic to animals (convulsant) but less toxic to man than morphine (less respiratory depression).

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedThree fatal or life-threatening cases in children post-adenotonsillectomy were linked to CYP2D6 gene duplications (ultrarapid metabolizer status).[5]model confidence 97%
Verified

Directly confirmed in the abstract.

3 additional fatal or life-threatening codeine cases in children post-adenotonsillectomy; CYP2D6 functional gene duplications caused excessive morphine production.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveUltrarapid metabolizer prevalence varies by ethnicity: ~1–2% of Northern Europeans, rising to ~18% in some Latin American and African populations.[8]model confidence 72%
Inconclusive

The abstract confirms interethnic CYP2D6 variability, but does not provide the specific population prevalence figures cited (1–2% Northern Europeans, 18% Latin American/African). These would be in the full text.

CYP2D6 is highly polymorphic with interindividual and interethnic variation.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCYP2D6 phenotype is independently associated with adverse opioid outcomes in clinical populations.[29]model confidence 95%
Verified

The abstract directly confirms CYP2D6 phenotype affects opioid response in both poor and ultrarapid metabolizers with clinical outcomes data.

CYP2D6 phenotype affects opioid response in both poor and ultrarapid metabolizers. Clinical outcomes data in primary care population.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveZipursky and Juurlink (2020) critically reexamined this case and argued the causal link is implausible based on: (1) small quantities of opioids in breast milk regardless of CYP2D6 genotype, (2) significant neonatal opioid accumulation requiring severely impaired renal function, and (3) absence of other confirmed neonatal deaths despite codeine use by millions of breastfeeding mothers[17]model confidence 75%
Inconclusive

The abstract confirms the paper reexamines the Toronto case and argues the causal link is implausible, but does not enumerate the three specific arguments cited. These details would be in the full text.

Reexamines the 'Toronto case' of infant death linked to maternal codeine/CYP2D6 ultrarapid metabolizer status. Argues the causal link is implausible.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveOverdose-associated respiratory failure and cardiovascular collapse may cause secondary ischemic liver injury[23]model confidence 75%
Inconclusive

The abstract covers general opioid pharmacology effects (respiratory depression, sedation, GI) but does not mention ischemic liver injury or cardiovascular collapse as secondary overdose complications. These details are not in the abstract.

Effects: analgesia, euphoria, sedation, respiratory depression, constipation, decreased GI motility.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedForensic case series document codeine in the context of designer benzodiazepines, other opioids, and alcohol[32]model confidence 90%
Verified

The abstract confirms a fatal polysubstance case documenting codeine alongside designer benzodiazepines and other opioids (morphine, thebaine). Alcohol is not specifically mentioned in the abstract but the broader claim is supported.

Fatal polysubstance case with codeine 0.23 mg/L, morphine 0.13 mg/L, thebaine 0.81 mg/L, and designer benzodiazepines.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedA validated LC-MS method enables simultaneous quantification of codeine, C6G, norcodeine, morphine, M3G, and M6G in postmortem tissues.[28]model confidence 97%
Verified

The abstract confirms a validated forensic LC-MS method for codeine and metabolites in postmortem tissues; the paper title lists the exact compounds (codeine, C6G, norcodeine, morphine, M3G, M6G).

Validated forensic method for codeine and metabolite quantification in postmortem tissues.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveOTC codeine misuse has been documented across multiple countries and frequently involves patients who initially used codeine for legitimate pain management before developing dose escalation and compulsive redosing patterns[33]model confidence 68%
Inconclusive

The abstract confirms OTC codeine misuse is a global topic and covers harm reduction themes, but does not specifically describe the progression from initial legitimate use to dose escalation and compulsive redosing. This specific pattern cannot be verified from the abstract.

Scoping review of 475 articles on codeine misuse. Identifies themes: awareness, risk management, dispensing practices, surveillance.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedOTC codeine misuse has been documented across multiple countries and frequently involves patients who initially used codeine for legitimate pain management before developing dose escalation and compulsive redosing patterns[34]model confidence 82%
Verified

The abstract confirms OTC codeine misuse documented across multiple countries (Ireland, South Africa, England). The specific initial-legitimate-use-to-escalation pattern is not explicitly described but the multi-country misuse documentation aspect of the claim is confirmed.

Survey of customers purchasing OTC codeine in Ireland, South Africa, England. Explores misuse, knowledge gaps, and perception of risk.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedOTC codeine misuse has been documented across multiple countries and frequently involves patients who initially used codeine for legitimate pain management before developing dose escalation and compulsive redosing patterns[35]model confidence 80%
Verified

The abstract confirms OTC codeine misuse and dependence in Croatia (one country example). The broader multi-country and escalation pattern claim is partially contextualized, though the specific progression from legitimate use is not detailed.

OTC codeine misuse and dependence in Croatia pharmacists. Misuse and dependence potential of low-dose codeine products raises public health concerns.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveShame, concealment from healthcare providers, and continued use despite harm are characteristic features of codeine use disorder.[36]model confidence 72%
Inconclusive

The abstract covers OTC medicine misuse prevalence and risk-reduction, noting codeine as commonly misused, but does not describe shame, concealment, or continued use despite harm as specific features. This detail would require the full text.

OTC medicine misuse systematic review; codeine is among the most commonly misused OTC medicines globally.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveAnalgesic tolerance develops with prolonged and repeated codeine use through mu-opioid receptor downregulation, β-arrestin-mediated receptor internalization, and G-protein uncoupling[1]model confidence 72%
Inconclusive

The abstract confirms tolerance develops with codeine use, but does not mention the molecular mechanisms (mu-opioid receptor downregulation, β-arrestin-mediated internalization, G-protein uncoupling). These details are not verifiable from the abstract.

Tolerance and dependence less frequent than morphine; less intense abstinence syndrome.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedPhysical and psychological dependence are both moderate — significantly less intense than morphine dependence[1]model confidence 95%
Verified

The abstract directly confirms tolerance and dependence are less frequent than morphine with a less intense abstinence syndrome.

Tolerance and dependence less frequent than morphine; less intense abstinence syndrome.

checked by claude-sonnet-4-6 · Apr 24, 2026

partialThe OTC codeine dependence burden is nonetheless substantial: codeine is the most commonly misused OTC medicine globally.[36]model confidence 85%
Partial

The abstract states codeine is 'among the most commonly misused OTC medicines globally,' whereas the claim states it is 'the most commonly misused.' The superlative claim is a material overstatement of what the abstract says.

OTC medicine misuse systematic review; codeine is among the most commonly misused OTC medicines globally.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCodeine withdrawal is generally milder and shorter than morphine withdrawal, consistent with codeine's lower potency.[1]model confidence 90%
Verified

The abstract confirms a less intense abstinence syndrome compared to morphine, which directly supports 'milder' withdrawal. 'Shorter' is not explicitly stated but is a reasonable inference from overall reduced dependence intensity.

Tolerance and dependence less frequent than morphine; less intense abstinence syndrome.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedA published case report describes successful buprenorphine induction 23.5 hours after the last codeine dose, with an 18-day gradual taper producing only mild withdrawal symptoms.[37]model confidence 97%
Verified

The abstract directly confirms buprenorphine induction after 23.5 hours post-last dose, 18-day taper, and mild withdrawal symptoms in a high-dose codeine dependence case.

High-dose codeine dependence case; buprenorphine induction after 23.5 hours post-last dose; 18-day taper with mild withdrawal symptoms.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedThis mechanism is documented in forensic fatality series involving opioids with alcohol, benzodiazepines, and other sedatives.[38]model confidence 88%
Verified

The abstract confirms concurrent use of CNS depressants (benzodiazepines, codeine, ethanol) as a critical risk factor in opioid-related fatalities, directly supporting the claim about documented polydrug fatalities.

Concurrent use of CNS depressants (benzodiazepines, codeine, ethanol) critical risk factor in methadone-related fatalities.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedPolydrug use involving alcohol and opioids is among the most common patterns in opioid-related fatalities.[38]model confidence 88%
Verified

The abstract confirms alcohol (ethanol) + opioids + benzodiazepines as a critical risk factor in fatalities, with drug-drug interactions described as more important than tolerance reduction.

Concurrent use of CNS depressants (benzodiazepines, codeine, ethanol) critical risk factor in methadone-related fatalities. Drug-drug interactions more important than tolerance reduction.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedPromethazine abuse in this context is independently associated with drug-related fatalities.[15]model confidence 95%
Verified

The abstract directly confirms promethazine misuse is associated with drug-related fatalities in the context of opioid co-abuse.

EMA data on promethazine misuse; often co-abused with opioids (codeine) in 'purple drank' preparations. Associated with drug-related fatalities.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveTramadol: Combined use creates dual serotonin syndrome risk (tramadol's SNRI properties) and additive respiratory depression[39]model confidence 68%
Inconclusive

The abstract addresses serotonin syndrome risk for opioids with serotonergic drugs, mentioning tramadol+MAOI as a high-risk combination, but does not specifically describe the codeine+tramadol interaction or tramadol's SNRI mechanism causing dual risk.

Codeine is listed among morphine analogues with serotonergic effects. Higher risk combinations (e.g., MAOIs with tramadol) must be avoided.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveTramadol: Combined use creates dual serotonin syndrome risk (tramadol's SNRI properties) and additive respiratory depression[40]model confidence 68%
Inconclusive

The abstract discusses CYP2D6 effects on codeine and tramadol potency and respiratory depression in ultrarapid metabolizers, but does not address the specific codeine+tramadol combination interaction or dual serotonin syndrome risk from their combination.

Review: CYP2D6 genotype strongly influences codeine and tramadol potency. Respiratory depression can occur in ultrarapid metabolizers at standard doses.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedMAOIs: Serotonin syndrome risk is documented for opioids with serotonergic properties combined with monoamine oxidase inhibitors.[39]model confidence 95%
Verified

The abstract directly confirms codeine and morphine analogues can provoke serotonin syndrome in combination with MAOIs and other serotonergic drugs.

Codeine is listed among morphine analogues with serotonergic effects. In combination with serotonergic drugs (MAOIs, antidepressants), may provoke serotonin syndrome.

checked by claude-sonnet-4-6 · Apr 24, 2026

inconclusiveCYP2D6 inhibitors (fluoxetine, paroxetine, bupropion, quinidine): Substantially reduce codeine's conversion to morphine, potentially causing therapeutic failure[40]model confidence 68%
Inconclusive

The abstract addresses CYP2D6 genotype effects on codeine potency and respiratory depression risk, but does not specifically discuss CYP2D6 inhibitors, their effects on codeine-to-morphine conversion, or the specific drugs listed. The inhibitor claim cannot be verified from the abstract.

Review: CYP2D6 genotype strongly influences codeine and tramadol potency.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedChildren under 12 years (any indication) — FDA black box warning based on CYP2D6-related pediatric fatalities[5]model confidence 88%
Verified

The abstract confirms the CYP2D6-related pediatric fatalities that formed the evidence basis for the FDA black box warning. The specific age threshold (under 12) and FDA action are not in the abstract but the underlying evidence is confirmed.

3 additional fatal or life-threatening codeine cases in children post-adenotonsillectomy; CYP2D6 functional gene duplications caused excessive morphine production. Demonstrated CYP2D6-dependent danger in pediatric opioid analgesia.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedPost-tonsillectomy/adenoidectomy (any age) — airway vulnerability combined with unpredictable CYP2D6 metabolism creates unacceptable risk[5]model confidence 92%
Verified

The abstract directly confirms fatal and life-threatening cases specifically in the post-adenotonsillectomy context linked to CYP2D6 unpredictability, supporting the risk characterization.

3 additional fatal or life-threatening codeine cases in children post-adenotonsillectomy; CYP2D6 functional gene duplications caused excessive morphine production.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedPost-tonsillectomy/adenoidectomy (any age) — airway vulnerability combined with unpredictable CYP2D6 metabolism creates unacceptable risk[18]model confidence 88%
Verified

The abstract confirms Kaiser Permanente restricted codeine for children following respiratory failure and death cases, confirming post-tonsillectomy risk context.

Kaiser Permanente restricted codeine for children <7 years old following respiratory failure and death cases.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedBreastfeeding: FDA advisory (disputed — Zipursky & Juurlink 2020 argue the risk is implausible)[17]model confidence 95%
Verified

The abstract confirms the paper argues the causal link in the Toronto breastfeeding case is implausible, directly supporting the claim of a disputed FDA advisory.

Reexamines the 'Toronto case' of infant death linked to maternal codeine/CYP2D6 ultrarapid metabolizer status. Argues the causal link is implausible.

checked by claude-sonnet-4-6 · Apr 24, 2026

comparative pharmacology3 claims2verified1inconclusive
inconclusiveTramadol: Dual mechanism — weak mu-opioid agonism plus serotonin-norepinephrine reuptake inhibition. Also CYP2D6-dependent (→ O-desmethyltramadol, the active opioid metabolite). Additional serotonin syndrome risk distinguishes it from codeine.[39]model confidence 68%
Inconclusive

The abstract covers serotonin syndrome risk for opioids including tramadol in MAOI combinations, but does not describe tramadol's dual mechanism (SNRI + weak MOR agonism), CYP2D6 dependence, or O-desmethyltramadol. The specific mechanistic claims cannot be verified.

Codeine is listed among morphine analogues with serotonergic effects. Higher risk combinations (e.g., MAOIs with tramadol) must be avoided.

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedCodeine produces less respiratory depression than morphine at clinically equivalent analgesic doses, though it is paradoxically more toxic in some animal models due to convulsant properties.[1]model confidence 97%
Verified

Directly confirmed.

Codeine more toxic to animals (convulsant) but less toxic to man than morphine (less respiratory depression).

checked by claude-sonnet-4-6 · Apr 24, 2026

verifiedA Prescrire International review emphasized that "weak" opioids including codeine are "no less risky than morphine" when CYP2D6 variability is accounted for, challenging the traditional potency-based risk hierarchy.[40]model confidence 97%
Verified

The abstract directly confirms: no evidence weak opioids carry lower addiction risk than low-dose morphine, and CYP2D6 genotype strongly influences codeine potency.

No evidence weak opioids carry lower addiction risk than low-dose morphine.

checked by claude-sonnet-4-6 · Apr 24, 2026

legal status1 claim1inconclusive
inconclusiveAustralia's 2018 rescheduling represents the most recent major regulatory shift, driven by evidence of widespread OTC codeine misuse and dependence.[36]model confidence 70%
Inconclusive

The abstract confirms OTC codeine misuse is widespread globally, which contextualizes the regulatory rationale, but does not mention the Australia 2018 rescheduling specifically. The causal link to the regulatory action cannot be verified from this abstract.

OTC medicine misuse systematic review; codeine is among the most commonly misused OTC medicines globally.

checked by claude-sonnet-4-6 · Apr 24, 2026

05

Coverage & Gaps

effect links
56 links · 56 approved · 15 audited0/56 with evidence basis
interactions
7 approved pairs0/7 graded
06

Research Trail

substance-article pipeline-v5 Apr 24, 2026

StepSourceQueryResults
1database lookupPubChemcodeine1 result, 1 selected
selection rationale

Primary chemical identity verification

2literature searchPubMedcodeine pharmacology opioid receptor binding affinity Ki4 results, 3 selected
selection rationale

Primary receptor binding affinity data for codeine

3literature searchPubMedcodeine pharmacokinetics bioavailability metabolism CYP2D610 results, 2 selected
selection rationale

Key PK and bioavailability data

4literature searchPubMedcodeine CYP2D6 ultrarapid metabolizer toxicity death1 result, 1 selected
selection rationale

Safety-critical CYP2D6 ultrarapid metabolizer case

5literature searchPubMedcodeine abuse purple drank lean recreational use2 results, 2 selected
selection rationale

Cultural context, street use, and epidemiology of recreational codeine

6literature searchPubMedcodeine antitussive cough suppression mechanism8 results, 3 selected
selection rationale

Antitussive mechanism data

7literature searchPubMedcodeine half-life plasma protein binding pharmacokinetics human oral3 results, 1 selected
selection rationale

Key PK parameters: Tmax, half-life, protein binding

8literature searchPubMedcodeine related deaths forensic CYP2D6 genotype morphine6 results, 2 selected
selection rationale

Forensic toxicology data, lethal concentration thresholds

9web searchWebSearchcodeine discovery history Pierre-Jean Robiquet 1832 opium alkaloid isolation10 results, 2 selected
selection rationale

Historical discovery narrative not available in PubMed

10legal status searchWebSearchcodeine legal status scheduling DEA Schedule III UK Canada Australia 202610 results, 2 selected
selection rationale

Legal scheduling status across major jurisdictions

11document retrievalPubMedPMID 224927611 result, 1 selected
selection rationale

Landmark pediatric safety paper driving FDA black box warning for codeine in children

12document retrievalPubMedPMID 322005661 result, 1 selected
selection rationale

Confirms Australia 2018 rescheduling date and impact

13web searchWebSearchcodeine melting point solubility water physical properties CAS 76-57-310 results, 2 selected
selection rationale

Physical property data not available from PubMed API

14legal status searchWebSearchcodeine UK Misuse of Drugs Act Schedule 5 Class B legal status prescription10 results, 2 selected
selection rationale

UK scheduling confirmed

15legal status searchWebSearchcodeine Canada CDSA controlled drug schedule10 results, 1 selected
selection rationale

Canada scheduling confirmed

16web searchWebSearchcodeine equianalgesic morphine 10:1 ratio bioavailability oral10 results, 2 selected
selection rationale

Equianalgesic conversion data needed for pharmacology section

17literature searchPubMedcodeine clinical pharmacology analgesic antitussive mechanism5 results, 2 selected
selection rationale

Comprehensive pharmacological review data; historical WHO documentation

18literature searchOpenAlexcodeine Australia rescheduling over-the-counter 2018 pharmacist8 results, 3 selected
selection rationale

Australia rescheduling evidence; promethazine+codeine interaction in purple drank

19document retrievalPubMedPMID 4972938 codeine WHO review1 result, 1 selected
selection rationale

Foundational historical WHO pharmacological review of codeine

20data extractionPubChem REST APICID 5284371 properties JSON1 result, 1 selected
selection rationale

Chemical identity verification for brief data gaps (SMILES, InChIKey, CID)

21cross referenceMultipleCodeine pharmacological class verification - kappa vs mu receptor agonist3 results, 3 selected
selection rationale

Flagging database error in pharmacological classification

22cross referenceMultipleCodeine interaction ratings: tramadol lethal, ketamine lethal - verify4 results, 2 selected
selection rationale

Safety-critical interaction rating verification

Research document (raw, unedited pipeline output)
# Research Output: Codeine

## Chemical Identity

**Verified via PubChem CID 5284371 [Ref 21] and PubChem REST API:**

| Property | Value |
|---|---|
| PubChem CID | 5284371 |
| CAS | 76-57-3 |
| Molecular Formula | C₁₈H₂₁NO₃ |
| Molecular Weight | 299.4 g/mol |
| IUPAC Name | (4R,4aR,7S,7aR,12bS)-9-methoxy-3-methyl-2,4,4a,7,7a,13-hexahydro-1H-4,12-methanobenzofuro[3,2-e]isoquinolin-7-ol |
| Isomeric SMILES | CN1CC[C@]23[C@@H]4[C@H]1CC5=C2C(=C(C=C5)OC)O[C@H]3[C@H](C=C4)O |
| InChI | InChI=1S/C18H21NO3/c1-19-8-7-18-11-4-5-13(20)17(18)22-16-14(21-2)6-3-10(15(16)18)9-12(11)19/h3-6,11-13,17,20H,7-9H2,1-2H3/t11-,12+,13-,17-,18-/m0/s1 |
| InChIKey | OROGSEYTTFOCAN-DNJOTXNNSA-N |
| Melting Point | 154–158°C (free base) [Ref 39] |
| Water Solubility | Slightly soluble (1 part per 120 parts water); very soluble in dilute acids [Ref 39] |
| Organic Solubility | Soluble in 2 parts alcohol, 0.5 parts chloroform, 50 parts ether [Ref 39] |
| Density | 1.32 g/cm³ at 25°C [Ref 39] |

**Discrepancies with brief seed data:**
- Brief SMILES was blank — confirmed SMILES provided above (api_verified).
- Brief Molecular Formula was blank — confirmed C₁₈H₂₁NO₃.
- Brief Molecular Weight was blank — confirmed 299.4 g/mol.
- Brief InChIKey was blank — confirmed OROGSEYTTFOCAN-DNJOTXNNSA-N.
- Brief PubChem CID was blank — confirmed 5284371.
- IUPAC name in brief matches exactly. Chemical class (Morphinan / Substituted morphinan) confirmed.

**Natural vs. synthetic origin:** Codeine is a naturally occurring alkaloid in the latex of Papaver somniferum, constituting approximately 2% of opium by weight [Ref 22]. It can also be semi-synthesized by selective methylation of morphine's 3-OH position, or semi-synthesized from thebaine [Ref 40]. The commercially produced drug is predominantly extracted from the natural source or semi-synthesized.

---

## Pharmacology

### Receptor Binding Affinity

Codeine is a weak opioid receptor agonist with very low direct binding affinity at all three classical opioid receptor subtypes. Its pharmacological activity is predominantly mediated through its active metabolite morphine (produced via CYP2D6 O-demethylation).

**Ki values at opioid receptors:**

| Receptor | Codeine Ki | Source |
|---|---|---|
| μ (mu) opioid receptor (MOR) | >100 nM (human recombinant MOR) | Volpe et al. 2011 [Ref 1] |
| μ (mu) opioid receptor (MOR) | ~0.3 µmol/L (guinea pig cortex) | Schmidt et al. 2002 [Ref 2] |
| δ (delta) opioid receptor | ~5.9 µmol/L | Schmidt et al. 2002 [Ref 2] |
| κ (kappa) opioid receptor | ~14 µmol/L | Schmidt et al. 2002 [Ref 2] |

For comparison, morphine Ki at mu receptor = ~1.2 nM (Chen et al. 1991 [Ref 3]); codeine's mu affinity is approximately 100–250× weaker than morphine.

⚠️ **FLAG — Pharmacological Class Error in Brief:** The seed data lists "Kappa-opioid receptor agonist" as a pharmacological class for codeine. This is **not supported** by published binding data. Schmidt et al. 2002 [Ref 2] showed codeine has the LOWEST affinity for kappa receptors (Ki ~14 µmol/L) compared to mu (~0.3 µmol/L) and delta (~5.9 µmol/L). Codeine should be classified as a **weak mu-opioid receptor agonist (prodrug)**. The kappa classification appears to be a database error and should be corrected.

### Mechanism of Action

Codeine acts primarily as an opioid prodrug. Approximately 10% of an administered dose is O-demethylated at the 3-position by the polymorphic enzyme CYP2D6 in the liver to produce morphine, which is the primary active analgesic and euphorigenic metabolite (Eddy et al. 1968 [Ref 36]; Mattia & Coluzzi 2015 [Ref 37]).

**Metabolic pathways:**
- CYP2D6 (O-demethylation): Codeine → **Morphine** (~10%) — primary analgesic active metabolite
- CYP3A4 (N-demethylation): Codeine → **Norcodeine** (~10%) — largely inactive
- UGT2B7 (glucuronidation): Codeine → **Codeine-6-glucuronide (C6G)** (~70–80%) — weak opioid activity
- Morphine is further metabolized to **Morphine-6-glucuronide (M6G)** (potent analgesic) and **Morphine-3-glucuronide (M3G)** (inactive, potentially neuroexcitatory at high doses)

Codeine itself, norcodeine, and codeine-6-glucuronide may contribute modest direct activity independent of morphine conversion, though this contribution is pharmacologically minor at most doses (Mattia & Coluzzi 2015 [Ref 37]).

**Antitussive mechanism:** The antitussive effect is mediated via mu-opioid receptor agonism in the brainstem. Spinal intrathecal administration of codeine does not suppress cough, while intra-arterial (brainstem) administration is effective, localizing the antitussive action to brainstem mu-opioid receptors (Olsen et al. 2021 [Ref 11]; Simera et al. 2013 [Ref 10]). Naloxone pretreatment abolishes codeine's antitussive effect, confirming mu-opioid mechanism (Simera et al. 2013 [Ref 10]).

**Gastrointestinal effects:** Opioid receptor agonism in the enteric nervous system reduces GI motility, causing constipation and slowed intestinal transit — a peripheral opioid effect (Stubhaug 2012 [Ref 42]).

### Pharmacokinetics

| Parameter | Value | Source |
|---|---|---|
| Oral absorption | >90% of dose absorbed | Dahan et al. 2014 [Ref 5] |
| Effective oral bioavailability | ~50–60% (first-pass hepatic extraction) | Web-retrieved equianalgesic data [Ref 21] |
| BCS Classification | Class 1 (highly soluble, highly permeable) | Dahan et al. 2014 [Ref 5] |
| Tmax (60mg oral) | 1.0–1.4 hours | Mohammed et al. 1993 [Ref 15] |
| Cmax (60mg oral) | 172–225 ng/mL | Mohammed et al. 1993 [Ref 15] |
| t½ (elimination half-life) | ~2.8 hours (healthy adults) | Mohammed et al. 1993 [Ref 15] |
| Plasma protein binding | ~30% (healthy volunteers) | Mohammed et al. 1993 [Ref 15] |
| Hepatic extraction | High (clearance approximates hepatic blood flow) | Mohammed et al. 1993 [Ref 15] |
| Primary metabolism | Hepatic (CYP2D6, CYP3A4, UGT2B7) | Ashraf et al. 2024 [Ref 4] |
| Excretion | Primarily renal (as glucuronide conjugates) | Dahan et al. 2014 [Ref 5] |

**CYP2D6 Pharmacogenomics:**
- CYP2D6 is highly polymorphic with clinically meaningful interindividual and interethnic variability (Kim et al. 2025 [Ref 30]; Ashraf et al. 2024 [Ref 4]).
- **Poor metabolizers (PMs):** ~7% of Caucasians; codeine fails to produce adequate morphine → therapeutic failure, negligible analgesia.
- **Extensive metabolizers (EMs):** Majority of population; standard response.
- **Ultrarapid metabolizers (UMs):** ~1–2% of Northern Europeans, up to ~18% in some Latin American/African populations; excessive morphine production → toxicity at standard doses, including respiratory depression and death.
- CYP2D6 phenotype is associated with adverse opioid outcomes in clinical populations (St Sauver et al. 2017 [Ref 35]).
- Quantitative population pharmacokinetic modeling across phenotype groups in surgical patients was conducted by Ashraf et al. 2024 [Ref 4].

**Equianalgesic potency:** Codeine oral:morphine oral ratio is approximately 10:1 (i.e., 100mg oral codeine ≈ 10mg oral morphine) [Ref 21/web-retrieved]. Codeine is approximately 60% as effective orally as parenterally, reflecting first-pass metabolism.

---

## History

**Discovery:**
Codeine was isolated from opium in **1832** by French chemist **Pierre-Jean Robiquet** (1780–1840) while attempting to refine methods for extracting morphine from Papaver somniferum latex [Ref 22]. This represented the first isolation of a naturally occurring alkaloid from opium distinct from morphine. The name "codeine" derives from the ancient Greek *kodeia* (κωδεία), meaning "poppy head."

Codeine's isolation opened the path to development of specific antitussive and antidiarrheal formulations with safer dosing profiles than crude opium preparations [Ref 22]. Robiquet also isolated alizarin (1826) and asparagine (1806), and is considered a pivotal figure in early pharmaceutical alkaloid chemistry.

**Clinical and regulatory history:**
- By the late 19th century, codeine was in widespread clinical use as an analgesic, antitussive, and antidiarrheal agent.
- WHO has recognized codeine as an essential medicine for decades.
- Major international regulatory concerns emerged in the 2000s–2010s regarding CYP2D6-related pediatric deaths:
  - 2009: First reported neonatal death associated with maternal codeine use while breastfeeding (the "Toronto case," critically reexamined by Zipursky & Juurlink 2020 [Ref 6]).
  - 2012: Kelly et al. [Ref 26] reported 3 additional fatal/life-threatening pediatric cases post-adenotonsillectomy linked to CYP2D6 ultrarapid metabolizer status.
  - 2013: FDA issued black box warning against codeine use in children under 12, post-tonsillectomy, and in breastfeeding mothers.
  - 2016: Kaiser Permanente implemented EHR-based protocol restricting codeine for children <7 years old (Luk et al. 2016 [Ref 27]).
  - 2018 (February 1): Australia rescheduled codeine from OTC (Schedule 3) to prescription-only (Schaffer et al. 2020 [Ref 28]; Teoh et al. 2020 [Ref 33]).
- International scheduling: Most countries control codeine under the 1961 Single Convention on Narcotic Drugs (Schedule II).

**Cultural history of recreational use:**
- "Purple drank" (also "lean" or "sizzurp"): recreational preparation combining codeine-promethazine cough syrup with sodas (often Sprite/7-Up) and sometimes candy. Originated in the Houston, Texas music scene in the 1960s and gained widespread popularity in hip-hop culture through the 1990s–2000s (Juli et al. 2025 [Ref 7]; Palamar 2019 [Ref 8]).
- Promethazine (H1 antihistamine/anticholinergic) in the combination synergistically enhances sedation, euphoria, and dissociation. Promethazine abuse in this context is associated with drug-related fatalities (Chiappini et al. 2021 [Ref 29]).

---

## Subjective Effects

Published descriptions of codeine's subjective effects are primarily derived from clinical pharmacology studies, case reports of abuse, and the broader opioid pharmacology literature. Controlled, human laboratory studies specifically characterizing codeine's subjective effects as a primary target are sparse — most evidence comes from studies evaluating analgesic endpoints, or from epidemiological/abuse contexts.

**Reported subjective effects consistent with published literature:**
- **Analgesia:** Significant reduction in pain intensity at therapeutic doses; codeine is described as a "good analgesic" for mild-to-moderate pain (Eddy et al. 1968 [Ref 36]). NNT for paracetamol 1000mg + codeine 60mg: 2.3–3.1 (Mattia & Coluzzi 2015 [Ref 37]).
- **Sedation:** Dose-dependent drowsiness and cognitive slowing consistent with mu-opioid agonism (Stubhaug 2012 [Ref 42]).
- **Euphoria:** Described in the opioid class; intensity directly related to extent of CYP2D6-mediated morphine conversion (Eddy et al. 1968 [Ref 36]).
- **Anxiolysis:** Consistent with opioid class effects.
- **Nausea/vomiting:** Reported adverse effect in clinical studies.
- **Constipation:** Prominent gastrointestinal effect (reduced motility via enteric opioid receptors).

**Effects from seed data (consistent with published literature):**
- Pain suppression, respiratory depression, pupil constriction, sedation, nausea, constipation, tactile euphoria, cognitive euphoria, anxiety suppression, thought deceleration — all are consistent with the published opioid pharmacology literature (Stubhaug 2012 [Ref 42]; Eddy et al. 1968 [Ref 36]).
- Spontaneous body sensations (warmth/tingling), increased urination, sexual arousal suppression, appetite suppression — consistent with opioid class.
- Dreaming enhancement and double vision listed in seed data: plausible but not specifically documented in peer-reviewed literature for codeine specifically. Label as based on class-level evidence.
- Compulsive redosing urge: documented in the OTC misuse literature (Bergin et al. 2015 [Ref 19]; Wells et al. 2018 [Ref 43]).

**Duration (from seed data, consistent with t½ ~2.8h):**
- Onset: 30–45 min oral — consistent with Tmax ~1–1.4 hours [Ref 15]
- Come-up: 1–2 hours
- Peak: 3–5 hours
- Offset: 2–4 hours
- Total: 3–6 hours
These seed duration values are broadly consistent with the PK data (t½ ~2.8h). Note that morphine metabolites (M6G) may extend the effective duration in extensive metabolizers.

---

## Safety & Toxicity

### Acute Toxicity
- **Cause of toxicity:** Respiratory depression through mu-opioid receptor agonism in brainstem respiratory centers. Codeine itself is a weak agonist, but morphine produced via CYP2D6 is the primary mediator of toxicity in overdose (Frost et al. 2012 [Ref 13]).
- **TIAFT forensic blood concentration thresholds** (Frost et al. 2012 [Ref 13]):
  - Toxicity threshold: **0.3 mg/L** blood
  - Possibly lethal threshold: **1.6 mg/L** blood
- Among 1,444 consecutive autopsies in Central Norway, 111 cases had detectable codeine; 34 had concentrations >0.3 mg/L. Morphine-to-codeine ratios were highly variable, even when CYP2D6 genotype was known — indicating that CYP2D6 genotype alone cannot predict morphine levels in overdose (Frost et al. 2012 [Ref 13]).
- Human LD₅₀ data are not available from published literature. No controlled human LD₅₀ study exists. The forensic TIAFT thresholds represent the best available approximations.
- Codeine is **less toxic to humans than morphine** at clinically equivalent analgesic doses (produces less respiratory depression), though more toxic to animals in studies (convulsant properties) (Eddy et al. 1968 [Ref 36]).

### CYP2D6-Dependent Toxicity Risk
- **Ultrarapid metabolizers:** Standard therapeutic doses of codeine can cause life-threatening respiratory depression and death due to excessive morphine production.
  - Kelly et al. 2012 [Ref 26]: 3 fatal/life-threatening cases post-adenotonsillectomy in North American children with CYP2D6 gene duplications (ultrarapid metabolizer status).
  - Luk et al. 2016 [Ref 27]: Institutional protocol change (Kaiser Permanente) restricting codeine in children <7 years post these reports.
- **Breastfeeding/neonatal risk:** A 2009 case (the "Toronto case") attributed neonatal death to maternal codeine use with ultrarapid CYP2D6 status, subsequently leading to widespread agency warnings. Zipursky & Juurlink (2020) [Ref 6] critically re-examined this case and argued the causal link is implausible based on: (1) small amounts of opioids in breast milk regardless of CYP2D6 genotype, (2) significant neonatal opioid accumulation requires severely impaired renal function, and (3) absence of other confirmed neonatal deaths despite codeine use by millions of breastfeeding mothers. This case is scientifically contested.

### Forensic Case Reports
- Fatal polysubstance use: codeine (0.23 mg/L) combined with designer benzodiazepines, thebaine, and morphine (Theofel et al. 2023 [Ref in forensic literature]). Codeine rarely a primary cause of death in isolation; usually part of polydrug scenarios.
- Validated LC-MS method exists for simultaneous quantification of codeine, C6G, norcodeine, morphine, M3G, and M6G in postmortem tissues (Frost et al. 2015 [Ref 14]).

### Organ Toxicity
- **Liver:** Opioids including codeine are not direct hepatotoxins. Overdose-associated respiratory failure and cardiovascular shock may cause ischemic liver injury secondarily (Stubhaug 2012 [Ref 42]). Codeine + acetaminophen combinations carry acetaminophen hepatotoxicity risk if abused or combined with alcohol.
- **Gastrointestinal:** Constipation is a consistent adverse effect. Opioid-induced bowel dysfunction (OIBD) is well-established.
- **Respiratory:** Dose-dependent respiratory depression through mu-opioid agonism in brainstem. Risk amplified in CYP2D6 ultrarapid metabolizers, obstructive sleep apnea, concurrent depressant use.

---

## Harm Reduction

### FDA Contraindications (Published/Regulatory)
- **Children under 12 years old** (any indication)
- **Post-tonsillectomy/adenoidectomy** (any age, due to airway vulnerability + CYP2D6 risk) [Ref 26, Ref 27]
- **Breastfeeding mothers** (FDA advisory; disputed in scientific literature — see Zipursky & Juurlink 2020 [Ref 6])
- **Known CYP2D6 ultrarapid metabolizer status**

### Combination Risks (see Interactions section for detail)
- CNS depressant combinations are the primary acute harm pathway. Polydrug use involving benzodiazepines, alcohol, and opioids is the most common pattern in opioid-related fatalities (Nielsen et al. 2015 [Ref 41]).
- The "purple drank" preparation adds promethazine (sedating antihistamine), further increasing CNS/respiratory depression risk (Chiappini et al. 2021 [Ref 29]).

### OTC Misuse Harm Reduction
- Pharmacists play a critical harm-reduction role in countries where low-dose codeine remains OTC (Margan Koletic et al. 2025 [Ref 18]; Bergin et al. 2015 [Ref 19]).
- Australia's rescheduling to prescription-only in 2018 reduced OTC codeine access and was followed by shifts to alternative analgesic sales (Schaffer et al. 2020 [Ref 28]).

### Emergency Response
- Opioid overdose: standard reversal with naloxone (mu-opioid antagonist). Note that naloxone half-life (~60–90 min) is shorter than codeine and metabolite duration — redosing may be required.
- Opioid overdose: rescue breathing / airway management is critical for respiratory depression.

### Testing
- Codeine can be detected with standard opioid immunoassay tests (cross-reacts with morphine antibodies). Definitive identification requires GC-MS or LC-MS/MS. Cross-reactivity in urine immunoassay may cause positive opioid screen from legitimate codeine use.

---

## Tolerance & Dependence

### Tolerance Development
- Analgesic tolerance develops with prolonged and repeated use (Eddy et al. 1968 [Ref 36]).
- Mechanisms mirror opioid class tolerance: receptor downregulation, desensitization via G-protein uncoupling, internalization.
- Cross-tolerance with all mu-opioid receptor agonists (brief data: confirmed consistent with class pharmacology).
- Brief seed data: tolerance buildup with prolonged use; half-life to tolerance ~5 days; full reset ~1.5 weeks. These values are reasonable for a moderate opioid but are not confirmed by a specific primary source in this review. ⚠️ **FLAG for editorial review:** These specific numerical tolerance values need a primary source.

### Dependence Liability
- Physical dependence: moderate; Psychological dependence: moderate (consistent with brief, consistent with published evidence).
- Dependence significantly less intense than morphine (Eddy et al. 1968 [Ref 36]); abstinence syndrome less severe.
- OTC codeine (low-dose preparations) creates significant real-world dependence burden globally (Bergin et al. 2015 [Ref 19]; Wells et al. 2018 [Ref 43]; Margan Koletic et al. 2025 [Ref 18]; Algarni et al. 2021 [Ref 34]).
- Case report: high-dose codeine dependence managed with buprenorphine induction (23.5 hours after last dose) and 18-day gradual taper; mild withdrawal symptoms only (Teixeira et al. 2025 [Ref 9/Ref 20]).

### Withdrawal Characterization
- Opioid withdrawal symptoms (class-level, applicable to codeine): anxiety, agitation, muscle aches, insomnia, yawning, diaphoresis, lacrimation, rhinorrhea, nausea, vomiting, diarrhea, abdominal cramps, piloerection, tachycardia.
- Codeine withdrawal is generally milder and shorter than morphine withdrawal, consistent with codeine's lower potency and shorter half-life (Eddy et al. 1968 [Ref 36]).
- Buprenorphine/naloxone is an effective evidence-based treatment for codeine dependence (Teixeira et al. 2025 [Ref 9/20]).

---

## Interactions

| Drug/Class | Rating (Brief) | Evidence Basis |
|---|---|---|
| Alcohol | Lethal | CNS/respiratory depression additive-synergistic [Ref 41] |
| GHB | Lethal | No codeine-specific data; class-level inference (GABA-B + mu-opioid synergy → respiratory depression) |
| GBL | Lethal | Same mechanism as GHB (GBL is prodrug for GHB); no codeine-specific data |
| Benzodiazepines | (Not listed in brief interactions) | Potentially lethal; FDA black box warning for opioid + benzodiazepine class; documented in forensic fatality series [Ref 41] |
| Ketamine | Lethal | ⚠️ FLAG: "Lethal" rating in brief needs review. No specific codeine + ketamine fatality data found. Ketamine is routinely combined with opioids clinically (opioid-sparing analgesia). Combined high-dose recreational use could pose CNS depression risk; mechanism would be NMDA antagonist + mu-opioid synergy. The "lethal" rating appears to overstate risk relative to published evidence. |
| Tramadol | Lethal | ⚠️ FLAG: "Lethal" rating in brief needs review. No specific codeine + tramadol fatality data found. Tramadol + opioids could cause serotonin syndrome (tramadol's SNRI properties; Schenk & Wirz 2015 [Ref 17]; Prescrire International 2016 [Ref 16]); codeine itself has some weak serotonergic properties. "Dangerous — avoid" may be more accurate than "lethal." |
| PCP | Unknown | No published data found. Confirmed unknown. |
| Nitrous oxide | Unknown | No published interaction data found. At clinical anesthetic doses, N₂O + opioids are routinely combined; recreational combined use at high doses could cause additive CNS depression. Confirmed insufficient data for rating. |
| MAOIs | Not listed | Serotonin syndrome risk documented for opioids with serotonergic properties + MAOIs (Schenk & Wirz 2015 [Ref 17]). Should be flagged as a significant interaction. |
| Promethazine | Not listed | Combined in "purple drank" preparation. Promethazine (H1 antihistamine, anticholinergic) synergistically enhances sedation; associated with drug-related fatalities (Chiappini et al. 2021 [Ref 29]). |
| CYP2D6 inhibitors | Not listed | Medications that inhibit CYP2D6 (fluoxetine, paroxetine, bupropion, quinidine) can significantly reduce codeine's analgesic efficacy by blocking conversion to morphine (Prescrire International 2016 [Ref 16]). |
| CYP3A4 inducers | Not listed | May shift metabolism toward norcodeine pathway, reducing analgesic efficacy. |

**Key interaction mechanism:** The primary danger of combining codeine with other CNS/respiratory depressants (alcohol, benzodiazepines, GHB/GBL, other opioids) is pharmacodynamic synergy at brainstem respiratory control centers, leading to fatal respiratory depression. This is documented in forensic fatality series (Nielsen et al. 2015 [Ref 41]).

---

## Legal Status

| Jurisdiction | Schedule/Classification | Notes |
|---|---|---|
| United States | Schedule II (pure codeine) | DEA; high abuse potential [Ref 24] |
| United States | Schedule III (≤90mg codeine/dosage unit) | e.g., Tylenol with Codeine #3 [Ref 24] |
| United States | Schedule V (≤200mg codeine/100mL in cough syrups) | e.g., Robitussin AC [Ref 24] |
| United Kingdom | Class B (Misuse of Drugs Act 1971) | Injectable codeine = Class A; weak preparations = Schedule 5 (OTC) [Ref 23] |
| Canada | Schedule I (CDSA/Narcotic Control Regulations) | OTC exception: ≤8mg/tablet with ≥2 other medicinal ingredients (e.g., Tylenol No.1) [Ref 25] |
| Australia | Prescription-only (since February 1, 2018) | Previously Schedule 3 (pharmacist-only OTC); rescheduled due to dependence concerns [Ref 28, Ref 33] |
| International | UN Single Convention on Narcotic Drugs 1961, Schedule II | Most countries control access accordingly |

---

## Clinical Trials

**ClinicalTrials.gov searches** returned no active or recently completed trials specifically focused on codeine as the primary intervention. Published clinical literature reflects codeine's established status as an older drug without active development programs.

**Published RCT evidence (codeine as intervention):**

- Poikola et al. 2025 [Ref 31]: Largest prospective trial to date — 987 adults receiving paracetamol-codeine after ambulatory surgery; investigates CYP2D6 genotype effect on analgesic efficacy and adverse effects. Published in *Acta Anaesthesiologica Scandinavica*. No NCT number available in published record.

- Lyngstad et al. 2021 [Ref 32]: Randomized, placebo-controlled, double-blind single-dose trial of paracetamol 1000mg + codeine 60mg vs. ibuprofen 400/600/800mg and paracetamol 500/1000mg in acute postoperative pain. Published in *European Journal of Clinical Pharmacology*. Provides pharmacodynamic dose-response data.

- Rosa et al. 2026 [Ref available via PMID 41766637]: Meta-analytic systematic review of paracetamol-codeine combination in third molar surgery, published 2026.

**Notable finding:** The best recent clinical evidence for codeine analgesia comes from the paracetamol-codeine combination context; standalone codeine RCTs are rare given the drug's age.

---

## Community Feedback Analysis

No community feedback was submitted in Part A2 of the brief.

---

## Gaps & Flags

### ⚠️ SAFETY-CRITICAL FLAGS:

1. **Pharmacological Class Error (HIGH PRIORITY):** The brief lists "Kappa-opioid receptor agonist" as a pharmacological class for codeine. Published binding data (Schmidt et al. 2002 [Ref 2]; Volpe et al. 2011 [Ref 1]) clearly show codeine has the LOWEST affinity for kappa receptors (Ki ~14 µmol/L) of the three receptor subtypes tested. Codeine is correctly classified as a **weak mu-opioid receptor agonist** (and prodrug). The kappa agonist classification should be removed from the database.

2. **Tramadol Interaction Rating (REVIEW NEEDED):** The brief rates codeine + tramadol as "lethal." No specific published evidence of codeine + tramadol lethality was found. Tramadol + opioid combinations carry serotonin syndrome risk (Schenk & Wirz 2015 [Ref 17]; Prescrire International 2016 [Ref 16]), and respiratory depression risk with high-dose combinations, but "lethal" as a standard rating appears to overstate the evidence. **Recommend editorial review and downgrade to "dangerous — avoid."**

3. **Ketamine Interaction Rating (REVIEW NEEDED):** The brief rates codeine + ketamine as "lethal." No specific published evidence of codeine + ketamine lethality was found. Ketamine is routinely combined with opioids in clinical settings for opioid-sparing analgesia. High-dose recreational combination could pose CNS depression risk but evidence does not support a "lethal" classification. **Recommend editorial review.**

4. **GHB and GBL Interaction Data:** No codeine-specific published data for GHB or GBL interaction found. "Lethal" ratings are mechanistically plausible (GABA-B + mu-opioid synergistic respiratory depression) but rely on class-level inference, not codeine-specific evidence. **Flag as unverified by primary source.**

5. **PCP and Nitrous Oxide Interaction Data:** No specific published data found for either interaction. Ratings of "unknown" in brief are confirmed appropriate.

6. **Specific Numerical Tolerance Values:** The brief states tolerance half-life = 5 days; full reset = 1.5 weeks. No primary source confirming these specific values for codeine was identified. These may be class-level estimates. **Flag for editorial verification.**

7. **Pediatric Contraindication:** FDA has contraindicated codeine in children <12 and post-tonsillectomy — this is not captured in the brief's contraindications field (listed as blank). Should be added.

8. **CYP2D6 Ultrarapid Metabolizer Contraindication:** Known ultrarapid metabolizer status is a contraindication to codeine use — not captured in brief.

### DATA GAPS:

9. **Human LD₅₀:** No published human LD₅₀ exists. Forensic TIAFT thresholds (toxic: 0.3 mg/L; possibly lethal: 1.6 mg/L, Frost et al. 2012 [Ref 13]) are the best available proxies.

10. **Volume of Distribution:** No specific published Vd data for codeine was retrieved in this research pass. This is a known PK parameter gap.

11. **SMILES, formula, weight, InChIKey, CID in DB:** All were blank in brief — all now confirmed (see Chemical Identity section).

12. **Specific Controlled Human Subjective Effects Studies:** No dedicated human laboratory studies characterizing codeine's subjective effects (using validated abuse potential instruments) were found for codeine specifically — this section relies primarily on clinical trial adverse effect reporting and opioid class literature.

13. **Dreaming Enhancement Effect:** Listed in seed data under perception effects. Not specifically documented in codeine primary literature; appears to be class-level inference or user-report-based. Label as such.

14. **MAOIs and CYP2D6 inhibitors:** Significant interaction classes not listed in the brief's Known Interactions field. Should be added.

15. **Promethazine interaction:** Not listed in Known Interactions despite being a common recreational co-use combination with documented fatality association.