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Carfentanil Facts

Opioid; Depressant; Anilidopiperidine; Mu-opioid receptor agonist

Description

Carfentanil is a synthetic opioid of the anilidopiperidine class. It activates opioid receptors in the brain, suppressing pain signaling and depressing the drive to breathe.

Subjective effects include intense euphoria, pain suppression, heavy sedation, and a dissolving of anxiety. These effects are inferred entirely from opioid pharmacology — no controlled human data exist, and the onset-to-loss of consciousness window may be measured in seconds.

Dependence liability is high, and the estimated lethal dose of roughly 20 µg[1] leaves no margin between an active and a fatal dose. Standard naloxone often fails — carfentanil binds opioid receptors in ways that resist displacement,[2] its effects outlast naloxone by hours,[3] and blood concentrations in survivors and fatalities overlap.[4][5]

Dose and durationby route · individual sensitivity varies

Insufflated

No dose recorded for this route. The timings are not a dose guide.

Starts in 1 – 5 minLasts 4 – 10 hours

Body and dependence

Acute toxicity
Critical
Chronic toxicity
Critical
Physical dependence
High
Psychological dependence
High
Withdrawal
Severe · medical supervision
Compulsive redosing
High

Tolerance

Builds
Rapid
Fully resets after
14 days
Carries over to
morphine; fentanyl; heroin; oxycodone; hydromorphone; methadone

Effectslikely at a common dose

Perception
none likely · 5 possible, including Spatial disorientation, Visual acuity suppression, Visual haze / noise
Body
Bodily heaviness; Body high; Breathing alteration; Constipation; Motor control impairment; Muscle relaxation; Pain suppression; Physical fatigue; Pupil constriction; Respiratory depression; Sedation; +12 possible, including Nausea, Abnormal heartbeat, Dizziness
Thinking
Analysis suppression; Cognitive fatigue; Cognitive impairment; Decision impairment; Focus suppression; Information processing suppression; Thought deceleration; +9 possible, including Memory suppression, Compulsive redosing urge, Confusion
Feeling
Euphoria; +4 possible, including Empathy suppression, Dysphoria
Self
none likely · 6 possible, including Communication suppression, Craving, Social disconnection
Time
none likely · 2 possible, including Temporal disorientation

Who shouldn't take it

Absolute
Respiratory compromise; Concurrent CNS depressant use; Absence of reversal agent access
Relative
Cardiovascular disease; Hepatic impairment; CYP3A4/3A5 inhibitor co-administration; Pregnancy

Combinations60 recorded

Lethal (4)
Benzodiazepines, Barbiturates; GHB, Baclofen; GHB, GBL; Local anesthetics
Dangerous (28)
Alpha-2 adrenergic receptor antagonist; Amphetamines; Anticholinergics; Antihistamines; Antipsychotics; Benzodiazepines; Buprenorphine, Kratom; Cannabis, THC; Clonidine, Guanfacine; Gabapentin, Pregabalin; MAOIs; MDMA, Amphetamines; MDMA, MDA; Naltrexone; NRIs; SNRIs; SSRIs; Stimulants; Synthetic cannabinoids; THC; Caffeine; CBD; Glutamate modulator; Huperzine A; and 4 more, see full page
Caution (19)
See full page: psychedex.org/substances/carfentanil
Not graded (9)
Not listed never means safe.

Seek help immediately if

  • Unresponsive / can't be woken, even to a firm sternal rub
  • Slow, shallow, or stopped breathing
  • Pinpoint pupils
  • Blue/grey lips, fingertips, or skin (cyanosis)
  • Limp body; pale, clammy skin
  • Choking or gurgling sounds ("death rattle")
  • Slow, erratic, or absent pulse

What to do

  1. Try to wake them — shout their name, firm sternal rub
  2. Call emergency services immediately
  3. Administer naloxone if available
  4. Give rescue breaths (or CPR if there is no pulse)
  5. Place them in the recovery position
  6. Stay with them; re-dose naloxone every 2–3 minutes if there is no response
Reversal agent
Naloxone (Narcan) — opioid antagonist. May require repeated doses; its effect can wear off before the opioid does.

With prompt naloxone and rescue breathing, reversal is usually rapid. Because naloxone can wear off before the opioid — especially with long-acting opioids (methadone) or high-potency ones (fentanyl) — a period of monitoring is needed even after the person revives.

988 Suicide & Crisis LifelineFireside Project: 62-FIRESIDE

Version r1 · Not medical advice

References

  1. [1]
    ^University of Bristol Chemistry Department (2018) Carfentanil: synthesis history, veterinary use, and illicit supply Link
  2. [2]
    ^Endt F, Guo T, Steinritz D, Amend N, Gudermann T, Breit A (2025) Carfentanil stabilizes µ opioid receptor conformations that are ultra-efficient in inhibiting cAMP, resistant to naloxone or nalmefene but sensitive to naltrexone — Archives of toxicology doi:10.1007/s00204-025-04048-6
  3. [3]
    ^Mann J, Samieegohar M, Chaturbedi A, et al. (2022) Development of a Translational Model to Assess the Impact of Opioid Overdose and Naloxone Dosing on Respiratory Depression and Cardiac Arrest — Clinical pharmacology and therapeutics doi:10.1002/cpt.2696
  4. [4]
    ^Kahl JH, Gonyea J, Humphrey SM, Hime GW, Boland DM (2018) Quantitative Analysis of Fentanyl and Six Fentanyl Analogs in Postmortem Specimens by UHPLC-MS-MS — Journal of analytical toxicology doi:10.1093/jat/bky054
  5. [5]
    ^Wallage HR, Elliot M, Rajotte JW (2022) Carfentanil Blood Concentrations in Impaired Driving Investigations in Ontario, Canada — Journal of analytical toxicology doi:10.1093/jat/bkac039
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