Hydromorphone

# Research Output: Hydromorphone

## Chemical Identity

**Confirmed via PubChem (CID 5284570) [Ref 22]:**

| Property | Value |
|---|---|
| Molecular formula | C₁₇H₁₉NO₃ |
| Molecular weight | 285.34 g/mol (free base); 321.80 g/mol (HCl salt) |
| CAS number (free base) | 466-99-9 |
| CAS number (HCl salt) | 71-68-1 |
| InChIKey | WVLOADHCBXTIJK-YNHQPCIGSA-N (stereospecific, PubChem) |
| IUPAC name (PubChem) | (4R,4aR,7aR,12bS)-9-hydroxy-3-methyl-1,2,4,4a,5,6,7a,13-octahydro-4,12-methanobenzofuro[3,2-e]isoquinolin-7-one |
| Systematic name | Morphinan-6-one, 4,5-epoxy-3-hydroxy-17-methyl-, (5α)- |
| SMILES (HCl) | `Cl.[H][C@@]12OC3=C(O)C=CC4=C3[C@@]11CCN(C)[C@]([H])(C4)[C@]1([H])CCC2=O` |

The brief's seed data (formula C₁₇H₁₉NO₃, MW 285.34) is **confirmed accurate**. The brief lacks CAS number, SMILES, and InChIKey — these are now supplied. PubChem CID is **5284570**, not listed in the brief.

**Structural notes:** Hydromorphone is a semi-synthetic morphinane (phenanthrene-type) opioid. It differs from morphine at C-6 (ketone substituted for hydroxyl) and lacks the C7–C8 double bond, and the C-3 hydroxyl of morphine is retained as the phenolic hydroxyl in hydromorphone. These modifications increase lipophilicity and MOR affinity relative to morphine.

**Stereochemistry:** The single active enantiomer is the (4R,4aR,7aR,12bS)- or (5α)-configuration. Only this levorotatory isomer is pharmacologically relevant. No data was found on the pharmacological activity of the (+)-enantiomer in humans.

---

## Pharmacology

### Receptor Binding

Hydromorphone is a **selective mu-opioid receptor (MOR) full agonist** with sub-nanomolar affinity [Ref 1][Ref 2].

- **MOR Ki < 1 nM** at recombinant human MOR (Volpe et al. 2011 [Ref 1]) — places hydromorphone in the highest-affinity tier alongside buprenorphine, oxymorphone, levorphanol, butorphanol, and sufentanil.
- **MOR Ki = 0.6 nM** in rat brain homogenates with [³H]-DAMGO (Chen et al. 1991 [Ref 2]), approximately twice the affinity of morphine (Ki = 1.2 nM) in the same assay.

A comprehensive receptor screen (Olson et al. 2019 [Ref 4]) tested hydromorphone against MOR, DOR, KOR, NOP, CB1, sigma-1R, and monoamine transporters (NET, SERT, DAT). No significant novel interactions beyond MOR were identified.

**FLAG — Pharmacological class discrepancy:** The brief lists "Kappa-opioid receptor agonist" as a pharmacological class. This is not supported by the primary literature. Hydromorphone is not characterized as a KOR agonist in any of the screened sources. The generation agent should propose removing "Kappa-opioid receptor agonist" from the pharmacological class.

### Signaling Bias

Manabe et al. (2019 [Ref 3]) reported that hydromorphone shows possible **G-protein pathway bias** relative to beta-arrestin2 recruitment at MOR. In cAMP and CellKey assays, hydromorphone was a potent full agonist (EC₅₀ between fentanyl and morphine), but its contribution to the internalization (beta-arrestin) pathway was smaller than morphine or fentanyl. The authors propose that this G-protein bias may contribute to hydromorphone's analgesic efficacy with potentially reduced adverse effects. Note: this is an in vitro finding; clinical confirmation of functional bias at therapeutic doses remains under investigation.

In comparative in vitro studies using NSO characterization panels, hydromorphone is routinely used as the reference agonist (100% Emax) against which other compounds are compared [Ref 4].

### Serotonin System

Hydromorphone **does not inhibit the human SERT or NET** in vitro (Baldo 2018 [Ref 29]; Rickli et al. 2018 [Ref 30]). This distinguishes it from opioids with serotonin syndrome liability (tramadol, tapentadol, meperidine, methadone). The FDA 2016 Drug Safety Communication on opioids and serotonin toxicity does not specifically implicate hydromorphone as a high-risk agent. Hydromorphone + serotonergic drugs combinations should still be used with caution given reports involving other opioids, but intrinsic serotonergic mechanism is not established for hydromorphone.

### Pharmacokinetics

**Oral administration:**
- Bioavailability: ~32% (range 17–62%) due to extensive first-pass hepatic metabolism (Bosilkovska et al. 2012 [Ref 28]; Vallner et al. 1981 [Ref 23])
- Onset: 15–30 minutes (StatPearls [Ref 25])
- Tmax (peak): 30–60 minutes for immediate-release (StatPearls [Ref 25])
- Duration: 3–4 hours per dose (immediate-release)
- Tmax (controlled-release): ~4.78 hours (Hagen et al. 1995 [Ref 16])

**FLAG — Duration data in brief:** The brief lists oral onset as "5–15 minutes" and peak as "15–20 minutes." Both are significantly faster than published data (onset 15–30 min, Tmax 30–60 min). These values require editorial correction.

**Intranasal administration:**
- Bioavailability: 52.4% (1 mg dose) and 57.5% (2 mg dose) (Coda et al. 2003 [Ref 9])
- Tmax: 20–25 minutes median
- Provides rapid, clinically meaningful absorption with ~2× higher bioavailability than oral; used for rapid onset in acute pain settings

**Intravenous administration:**
- Bioavailability: 100% (reference route)
- Onset: Rapid; analgesic effect within minutes
- Duration: 3–4 hours

**Distribution:**
- Volume of distribution: ~4 L/kg (StatPearls [Ref 25]); earlier data reported 1.22 L/kg (Vallner 1981 [Ref 23]) — discrepancy likely reflects compartmental modeling differences; newer value generally cited
- Plasma protein binding: 8–19% (low — clinically important for reduced drug–drug interactions via displacement) (Lussier et al. 2010 [Ref 8])

**Elimination half-life:**
- Immediate-release: 2–3 hours (2.64 ± 0.88 hours in Vallner 1981 [Ref 23])
- Extended-release (OROS): 8–15 hours (typically ~11 hours) (Carter & Keating 2010 [Ref 17])

**Metabolism:**
- Primary pathway: hepatic glucuronidation → **hydromorphone-3-glucuronide (H3G)** as the dominant metabolite
- H3G:hydromorphone molar ratio at steady state: **27:1** (Hagen et al. 1995 [Ref 16])
- H3G is **pharmacologically inactive as an analgesic** but is **neuroexcitatory** — dose-dependently causes allodynia, myoclonus, and seizures in rodents following ICV administration (Smith 2000 [Ref 5])
- Unlike morphine, hydromorphone **does not produce an active 6-glucuronide metabolite** (M6G equivalent) — this makes hydromorphone preferable over morphine in some renal failure patients (Lussier 2010 [Ref 8])
- CYP enzyme involvement: **minor**. Rifampin (CYP3A inducer) reduces hydromorphone plasma concentrations, but the effect is modest, confirming that CYP3A plays only a secondary metabolic role (Lohela et al. 2021 [Ref 7])
- Excretion: primarily renal (~7% unchanged drug in urine, ~1% in feces, remainder as glucuronides)

**Food effect:** Bioavailability of OROS hydromorphone is **not affected by food or ethanol** (Moore et al. 2011 [Ref 10]; Lussier 2010 [Ref 8]).

**Equianalgesic potency:** Oral hydromorphone is approximately **5× more potent than oral morphine** (conversion ratio: 5 mg oral morphine ≈ 1 mg oral hydromorphone). This ratio is supported by multiple RCTs and conversion studies (Hanna & Thipphawong 2008 [Ref 18]; Treillet et al. 2018 [Ref 27]; Coluzzi & Mattia 2010 [Ref 21]).

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## History

**Synthesis:** Hydromorphone was first synthesized in **Germany in 1921** and patented in **1923**. The synthesis was accomplished via catalytic hydrogenation of morphine, modifying the C6 hydroxyl to a ketone and reducing the C7–C8 double bond. Early references credit the discovery to chemists working in the German pharmaceutical industry, with the Knoll pharmaceutical company commercializing the drug [Ref 21 web].

**Clinical introduction:** Hydromorphone was introduced to clinical practice in **1926** under the brand name **Dilaudid** (coined to reflect its derivation from — and similarity to — morphine via laudanum) [web search, DEA fact sheet Ref 21]. Within 10 years of introduction, over 200 publications had appeared supporting its pain-relieving properties.

**Early positioning:** Despite its documented potency advantage over morphine, hydromorphone was historically positioned as a second-line analgesic, a status that persisted for most of the 20th century. It was approved in Japan more recently (noted in Manabe et al. 2019 [Ref 3]).

**Contemporary formulations:** The osmotic-controlled release oral delivery system (OROS) formulation — sold as Jurnista (outside USA) — was developed as a once-daily formulation delivering hydromorphone at a near-constant rate over 24 hours (Carter & Keating 2010 [Ref 17]).

**Regulatory history:** Under the US Controlled Substances Act (1970), hydromorphone was classified as **Schedule II**. No published sources document a specific prior scheduling change from a less-restricted status. International scheduling occurred in parallel across major jurisdictions.

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## Subjective Effects

### Published Descriptions

Walsh et al. (2008 [Ref 13]) conducted a double-blind RCT in 9 prescription opioid abusers comparing oral oxycodone, hydrocodone, and hydromorphone. Hydromorphone produced:
- Increased ratings of **drug liking**, **good drug effects**, **drug high**, and **opiate symptom scores** — all dose-related
- **Miosis** (pupillary constriction)
- Modest **respiratory depression**
- Exophoria and decrements in visual threshold discrimination

Hydromorphone was approximately equipotent in its abuse-liability profile to oxycodone and hydrocodone (only modestly more potent), which the authors noted was inconsistent with analgesic potency estimates.

Schlaepfer et al. (1998 [Ref 4-via PubMed]) confirmed that mu-opioid agonists (including hydromorphone) produce primarily **euphoria** (contrasted with kappa agonist-induced dysphoria), with anatomically distinct regional cerebral blood flow changes.

Mazer-Amirshahi et al. (2018 [Ref 14]) noted that **IV hydromorphone has particularly potent euphoric effects** — more pronounced than equivalent analgesic doses of morphine — which has contributed to escalating emergency department use and abuse concerns.

### Effect Profile Assessment

Based on published literature, the following effects from the brief's taxonomy are supported for hydromorphone:

**Body (well-documented):**
- **Sedation** — prominent, dose-dependent
- **Pain suppression** — primary therapeutic effect, mediated via MOR
- **Respiratory depression** — serious safety concern; dose-dependent
- **Constipation** — via peripheral MOR in GI tract; common with chronic use [Ref 20]
- **Nausea** — common, especially on initiation [Ref 20]
- **Pupil constriction** — consistent finding [Ref 13]
- **Tactile euphoria / body high** — reported in abuse contexts [Ref 13]
- **Muscle relaxation** — class effect
- **Vomiting** — may accompany nausea
- **Spontaneous body sensations** — warmth, flushing common
- **Sexual arousal suppression** — class effect via hypothalamic–pituitary axis suppression (hypogonadism with chronic use)
- **Appetite suppression** — class effect
- **Dry mouth** — class effect via anticholinergic-like GI effects
- **Dizziness** — common adverse effect

**Thinking/Feeling:**
- **Cognitive euphoria** — robust finding [Ref 13]
- **Anxiety suppression** — anxiolytic effect common with opioids
- **Compulsive redosing urge** — established with high-abuse-liability profile [Ref 13]
- **Cognitive impairment** — sedation-related
- **Memory suppression** — secondary to sedation

**Perception:**
- **Dreaming enhancement / internal hallucinations** — may occur especially at high doses or with H3G accumulation
- **Increased urination** — occasional

**Note on intensity/frequency values:** The brief lists all 16 effect slugs as having null intensity/frequency. Based on the literature:
- **Pain suppression, sedation, constipation, nausea, pupil constriction**: very high frequency (>80% of users in clinical settings), high intensity
- **Respiratory depression**: high clinical frequency at analgesic doses but severity varies with dose/tolerance
- **Tactile euphoria, cognitive euphoria, compulsive redosing urge**: moderate-to-high frequency in recreational/abuse contexts, high intensity
- **Sexual arousal suppression**: moderate frequency (primarily chronic use)
- **Dreaming enhancement, internal hallucinations, increased urination**: low-to-moderate frequency

---

## Safety & Toxicity

### Acute Toxicity

**LD50 data:** No specific human LD50 data found in published sources. The therapeutic index is narrow and toxic-to-therapeutic dose ratio is not well characterized in controlled studies. Case reports document fatalities at doses that would be therapeutic in opioid-tolerant individuals (indicating the critical role of tolerance in safety margin).

**Overdose presentation:** Includes altered consciousness/coma, respiratory depression (rate <12/min, apnea), miosis (though may be absent in mixed overdoses), cyanosis, hypotension, bradycardia. Severe cases progress to respiratory failure and death (StatPearls [Ref 25]).

**Treatment:** Naloxone 0.4–2 mg IV/IM/SC every 2–3 minutes (max ~10 mg total). Repeat dosing often required given hydromorphone's elimination half-life of 2–3 hours exceeds naloxone's ~30–90 minutes. Supportive ventilation as needed (StatPearls [Ref 25]).

### H3G Metabolite Risk

Hydromorphone-3-glucuronide (H3G) accumulates at a 27:1 molar ratio to hydromorphone at steady state (Hagen 1995 [Ref 16]). H3G is neuroexcitatory, producing allodynia, myoclonus, and seizures in animal models at intracerebroventricular doses (Smith 2000 [Ref 5]). In renal insufficiency, H3G plasma concentrations are ~4× higher than in patients with normal renal function (Paramanandam et al. 2011 [Ref 6]). Clinical reports of neuroexcitatory phenomena in patients receiving high-dose hydromorphone are documented. Opioid rotation away from hydromorphone (e.g., to methadone or fentanyl) typically resolves these symptoms over hours to days (Smith 2000 [Ref 5]).

### Organ Toxicity

**Respiratory:** Respiratory depression is the primary cause of opioid overdose death. Dose-dependent; significantly potentiated by alcohol, benzodiazepines, and other CNS depressants.

**GI:** Constipation is nearly universal with chronic use due to peripheral MOR agonism slowing GI motility. Hydromorphone may have marginally lower GI adverse effects than morphine in some comparisons (Wirz et al. 2008 [Ref 20]).

**Endocrine:** Chronic opioid use causes opioid-induced androgen deficiency (hypogonadism), leading to sexual dysfunction, infertility, depression, and decreased bone mineral density — class effect, not hydromorphone-specific.

**Hepatic:** Hydromorphone is primarily metabolized in the liver. In severe hepatic impairment, bioavailability increases and clearance decreases substantially, requiring dose reduction (Bosilkovska et al. 2012 [Ref 28]).

**Renal:** H3G accumulation in renal failure is the primary safety concern. Despite this, hydromorphone is often preferred over morphine in renal failure because it lacks the active morphine-6-glucuronide metabolite (Lussier 2010 [Ref 8]; Coluzzi et al. 2020 [Ref 19]). Careful monitoring and dose reduction required.

### Psychological Risks

- High addiction potential; DEA Schedule II classification reflects "high potential for abuse leading to severe psychological or physical dependence" [Ref 21]
- In opioid-naive individuals, a single euphorigenic dose can initiate craving and compulsive use [Ref 14]
- IV use is associated with particularly high abuse liability [Ref 11]

---

## Harm Reduction

### Published Risk Reduction Strategies

**Never combine with:**
- Alcohol — additive CNS/respiratory depression; lethal at relatively modest doses
- Benzodiazepines — synergistic respiratory depression; responsible for significant proportion of opioid overdose deaths
- GHB/GBL — CNS depressant combination; lethal risk
- Other opioids (unless directed by prescriber managing chronic pain)

**Overdose response:** Naloxone (Narcan) reverses hydromorphone overdose. Multiple doses may be needed. Recovery position while awaiting emergency services.

**Dose titration:** Start low, especially in opioid-naive individuals. The dose-response curve for respiratory depression is steeper than for analgesia in some populations.

**Renal monitoring:** In patients with renal impairment, H3G accumulation warrants monitoring for neuroexcitatory phenomena (myoclonus, seizures, allodynia). Consider opioid rotation if these occur (Smith 2000 [Ref 5]).

**Drug testing:** Hydromorphone is detectable in urine drug screens (immunoassay), typically for 2–4 days. May cross-react with morphine immunoassay; confirmation by GC-MS/LC-MS required for specificity.

### Contraindications (Published)

- Significant respiratory compromise (bronchial asthma, COPD with CO₂ retention)
- Gastrointestinal obstruction / paralytic ileus
- MAO inhibitor use within 14 days
- Known hypersensitivity to hydromorphone or sulfites (in some formulations)
- Concurrent use of CNS depressants without careful dose titration
- Pregnancy (neonatal opioid withdrawal syndrome; respiratory depression in neonate)

---

## Tolerance & Dependence

### Tolerance Development

Tolerance to hydromorphone's analgesic effects develops with repeated dosing, consistent with all mu-opioid agonists. The mechanism involves receptor desensitization (uncoupling from G-proteins), receptor internalization, and downstream neuroadaptation. Tolerance develops at differential rates for different effects: analgesic tolerance develops relatively quickly (days to weeks), while constipation tolerance develops more slowly if at all.

**Cross-tolerance:** Opioid cross-tolerance with other mu-opioid agonists is well established (morphine, oxycodone, fentanyl, heroin, etc.). The equianalgesic conversion ratio (5:1 oral morphine:hydromorphone) accounts for incomplete cross-tolerance, requiring dose reduction (typically 25–50%) when rotating opioids.

**Opioid substitution:** Hydromorphone has been used in opioid substitution treatment programs. A conversion study by Oviedo-Joekes et al. (2011 [Ref 12]) examined hydromorphone vs. diacetylmorphine (heroin) in substitution treatment for long-term opioid-dependent patients.

### Physical Dependence

Physical dependence develops with regular use (days to weeks). Abrupt discontinuation produces a withdrawal syndrome consistent with mu-opioid withdrawal: anxiety, restlessness, diaphoresis, tachycardia, mydriasis, myalgias, GI cramping, diarrhea, insomnia. Onset typically 4–12 hours after last dose (shorter than methadone), peak 36–72 hours, duration 5–10 days (acute phase) with protracted symptoms possible.

**Dependence liability:** Walsh et al. (2008 [Ref 13]) characterized oral hydromorphone's abuse-liability profile as comparable to oral oxycodone/hydrocodone. IV abuse liability is higher due to rapid central delivery and pronounced euphoria (Levy-Cooperman 2016 [Ref 11]; Mazer-Amirshahi 2018 [Ref 14]).

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## Interactions

### Lethal/High-Risk Combinations

**Alcohol (ethanol):** Additive CNS and respiratory depression. The OROS extended-release formulation bioavailability is not substantially altered by alcohol (unlike some ER morphine formulations), but pharmacodynamic interaction is present regardless. Alcohol is listed as a "lethal" interaction in the brief — this is well-supported by class pharmacology.

**GHB/GBL:** Both are CNS depressants with GABAergic mechanisms. Combination with opioids is known to dramatically potentiate respiratory depression. Listed as "lethal" — pharmacologically plausible, supported by class-level evidence.

**Ketamine:** At subanesthetic/recreational doses, additive CNS depression. At clinical doses, ketamine is used as an opioid-sparing agent. The "lethal" classification in the brief is likely overstated for clinical/moderate recreational doses; more accurately "dangerous" or "unpredictable."

**Tramadol:** Opioid combination risk (respiratory depression) plus tramadol's serotonergic mechanism (SERT inhibition). Listed as "lethal" — risk is via combined opioid effect + potential for tramadol-induced seizure lowering threshold. However, hydromorphone itself does not inhibit SERT (Baldo 2018 [Ref 29]).

**Nitrous oxide:** Listed as "unknown" in the brief. Nitrous oxide has CNS depressant properties but is short-acting. Combined with opioids in clinical anesthesia it is routine; recreational polysubstance risk is theoretical.

**PCP:** Listed as "unknown." PCP is a dissociative with NMDA receptor antagonism. Limited published data on specific hydromorphone–PCP interaction.

### Mechanism-Based Interactions

**MAO inhibitors (MAOIs):** Contraindicated. Risk of severe, potentially fatal serotonergic reactions and CNS depression. Mechanism unclear for phenanthrene opioids but extrapolated from class warnings (package insert data).

**CYP3A inducers (rifampin):** Reduce hydromorphone plasma concentrations, though the effect is moderate (Lohela et al. 2021 [Ref 7]).

**No significant SERT/NET interactions:** Unlike tramadol, meperidine, or methadone, hydromorphone does not inhibit serotonin reuptake (Baldo 2018 [Ref 29]; Rickli et al. 2018 [Ref 30]). Lower intrinsic serotonin syndrome risk as monotherapy or with typical serotonergic medications, though caution with serotonergic drugs is still advised per FDA guidance.

**CNS depressants (general):** Benzodiazepines, barbiturates, Z-drugs, muscle relaxants, antihistamines — all potentiate respiratory depression via additive mechanisms.

---

## Legal Status

| Jurisdiction | Schedule/Status | Notes |
|---|---|---|
| United States | DEA Schedule II (CSA) | High abuse potential; accepted medical use; no refills permitted [Ref 21, Ref 25] |
| United Kingdom | Class A (Misuse of Drugs Act 1971) | Also listed in Schedule 2 for prescription purposes |
| Canada | Schedule I (CDSA) | Available as prescription analgesic (Hydromorph Contin, Dilaudid) |
| Australia | Schedule 8 (Controlled Drug) | TGA regulated; prescription required |
| European Union | Most EU member states: strictly controlled narcotic | Equivalent to Schedule II; regulated under 1971 UN Convention |
| Germany | Betäubungsmittelgesetz (BtMG) — Anlage III | Most restricted medicinal drug schedule |
| Japan | Approved 2013 (narcotic) | Mentioned in Manabe et al. 2019 [Ref 3] |

**International treaty:** Hydromorphone is listed under **Schedule I of the 1961 UN Single Convention on Narcotic Drugs**, requiring parties to limit use to medical and scientific purposes.

**Note:** Legal status data is from web sources [Ref 21, web search]. Specific scheduling amendment dates were not found in published literature.

---

## Clinical Trials

**Key identified trials (via ClinicalTrials.gov search):**

| NCT ID | Title | Phase | Status | Conditions | Sponsor |
|---|---|---|---|---|---|
| NCT00803283 | OROS Hydromorphone HCl vs. Morphine SR in Cancer Pain | Phase 3 | TERMINATED | Cancer Pain | J&J Taiwan |
| NCT03893734 | Effect of Methadone and Hydromorphone on QT Interval After Surgery | Phase 4 | RECRUITING | QT Prolongation | Endeavor Health |

**Published key RCTs (not registered above but foundational):**
- Hanna & Thipphawong 2008 [Ref 18]: OROS hydromorphone vs. CR morphine in chronic cancer pain — demonstrated clinical equivalence
- Chang et al. 2009 [Ref 15]: "1+1" IV hydromorphone protocol in ED — safety and efficacy
- Walsh et al. 2008 [Ref 13]: Abuse liability and subjective effects RCT
- Chang et al. 2009 [Ref 31]: Hydromorphone vs. morphine in elderly ED patients — similar efficacy/safety

**Areas needing further clinical investigation:** Hydromorphone-specific data in neonates is lacking (Spenard et al. 2024 [Ref 26]); longer-term abuse liability outcomes in non-opioid-dependent populations; and formal dose-finding studies for the intranasal route.

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## Community Feedback Analysis

No community feedback was submitted in Part A2 of the brief for this substance. No community feedback items to evaluate.

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## Gaps & Flags

### 🚨 Critical Data Flags

**FLAG 1 — "Characterization: emerging" is INCORRECT:**  
Hydromorphone was first synthesized in 1921 and has been in clinical use since 1926. It is a well-established, widely-prescribed drug with over a century of published literature. The "emerging" characterization in the DB is a data entry error and must be corrected. Recommended correction: "well-established" or equivalent.

**FLAG 2 — "Primary ROA: insufflated" is clinically inaccurate:**  
The primary clinical ROA for hydromorphone is **oral** (tablets, ER capsules) and **intravenous** (in hospital/ED settings). Insufflation is a recreational/non-medical route. The brief likely reflects non-medical use patterns, which may be intentional for a harm reduction encyclopedia — but should be labeled clearly. If the database distinguishes "primary medical ROA" from "primary recreational ROA," this should be noted. Recommend editorial decision.

**FLAG 3 — "Kappa-opioid receptor agonist" in pharmacological class:**  
Primary literature does not characterize hydromorphone as a KOR agonist. Olson et al. 2019 [Ref 4] screened hydromorphone against KOR and found no significant activity. The MOR-selective profile is well-established. Recommended correction: remove "Kappa-opioid receptor agonist" from pharmacological class.

**FLAG 4 — Oral duration data discrepancies:**  
The brief lists oral onset as "5–15 minutes" and peak as "15–20 minutes." Published data consistently shows onset 15–30 minutes and Tmax 30–60 minutes for immediate-release formulations (StatPearls [Ref 25]). These values in the DB are significantly faster than documented and should be corrected.

**FLAG 5 — PubChem CID missing from brief:**  
PubChem CID is 5284570 — not present in seed data. Should be populated.

**FLAG 6 — SMILES/InChIKey missing from brief:**  
Both are now available and should be added to the DB record.

### Data Gaps (Not Resolvable from Published Literature)

- **Specific LD50 in humans:** No published LD50 data found. Toxicological estimates are inferred from clinical overdose reports, not controlled dose-escalation studies.
- **KOR binding Ki:** No published KOR-specific binding constant found for hydromorphone in primary sources. The absence of KOR activity is inferred from comprehensive screening panels.
- **Intranasal pharmacokinetics in subjects with rhinitis:** Coda 2003 [Ref 9] studied normal subjects; the Davis et al. 2004 [Ref 9] paper studied vasomotor rhinitis patients but the abstract was not fully retrieved.
- **Long-term neuropsychological effects:** No controlled studies found on cognitive or neuropsychological outcomes from long-term non-therapeutic hydromorphone use.
- **Drug interaction data specific to GHB, nitrous, PCP:** The "lethal" classifications for GHB/GBL and tramadol in the interactions table are pharmacologically well-justified at the class level, but no hydromorphone-specific published case series was retrieved. PCP interaction is unstudied.
- **Physical properties (melting point, solubility):** Not searched in detail; available from chemistry databases but not primary pharmacology literature.