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Fentanyl Facts

Opioid; Anilidopiperidine; Mu-opioid receptor agonist

Description

Fentanyl is a synthetic opioid of the anilidopiperidine family. It activates opioid receptors in the brain and spinal cord, suppressing pain signaling and producing sedation.

Subjective effects include profound pain suppression, euphoria, heavy sedation, and a warm dissolution of anxiety and distress.[1] The experience is defined by what it removes — discomfort disappears and the body settles into a weighted, quiet calm.

Fentanyl produces rapid physical dependence,[2] and the gap between an active dose and a fatal dose is among the narrowest of any commonly used drug.[3] Tolerance to pain relief builds faster than tolerance to breathing suppression, so dose escalation narrows the margin of safety.[4]

Dose and durationby route · individual sensitivity varies

Sublingual(µg)
Threshold< 12 µgLight12 – 25 µgCommon25 – 50 µgStrong50 – 100 µgHeavy100+ µg

Starts in 15 – 30 minLasts 1 – 4 hoursAfter-effects 2 – 6 hours

Body and dependence

Acute toxicity
Critical
Chronic toxicity
High
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; heroin; oxycodone; hydrocodone; methadone; codeine; hydromorphone; oxymorphone; buprenorphine

Effectslikely at a common dose

Perception
Sleep-transition hallucinations; +3 possible, including Spatial disorientation, Visual acuity suppression, Double vision
Body
Sedation; Pain suppression; Spontaneous body sensations; Respiratory depression; Constipation; Pupil constriction; Bodily heaviness; Body high; +16 possible, including Motor control impairment, Nausea, Excessive sweating
Thinking
none likely · 14 possible, including Cognitive impairment, Compulsive redosing urge, Analysis suppression
Feeling
Anxiety suppression; Euphoria; +2 possible, including Anhedonia
Self
none likely · 5 possible, including Craving, Communication suppression, Social disconnection
Time
none likely · 2 possible, including Temporal disorientation

Who shouldn't take it

Absolute
Respiratory insufficiency; Pregnancy; Paralytic ileus
Relative
Hepatic impairment; Elderly; Concurrent CNS depressant use; Concurrent gabapentinoid use; Concurrent CYP3A4 inhibitor use

Combinations62 recorded

Lethal (6)
Benzodiazepines, Barbiturates; GHB, Baclofen; GHB, GBL; Ketamine; Local anesthetics; Tramadol
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/fentanyl
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]
    ^Baylon GJ, Kaplan HL, Somer G, Busto UE, Sellers EM (2000) Comparative abuse liability of intravenously administered remifentanil and fentanyl — Journal of Clinical Psychopharmacology PMID:11106130
  2. [2]
    ^Hurle MA (2001) Changes in the expression of G protein-coupled receptor kinases and beta-arrestin 2 in rat brain during opioid tolerance and supersensitivity — Journal of Neurochemistry PMID:11299311
  3. [3]
    ^European Union Drugs Agency (EUDA) (2024) Fentanyl drug profile - European Union Drugs Agency (EUDA) Link
  4. [4]
    ^Rai KG et al. (2025) Divergent ventilatory responses during opioid-induced respiratory depression in response to repeated fentanyl use — American Journal of Physiology: Lung doi:10.1152/ajplung.00302.2024
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