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Acetylfentanyl

Acetylfentanyl molecule structureAcetylfentanyl molecule structure
N-(1-Phenethylpiperidin-4-yl)-N-phenylacetamide
Acetyl Fentanyl, Desmethyl Fentanyl
Psychoactive Class
Chemical Class

Acetylfentanyl is a synthetic opioid of the anilidopiperidine class and a structural analog of fentanyl.citation needed Originally described in the 1960s alongside fentanyl itself, it has never been approved for medical use and has only appeared on the illicit market as a designer drug. It is estimated to be several times more potent than heroin1 yet roughly fifteen times less potent than fentanyl, still presenting significant overdose risk.citation needed

Dosage & Duration

Dosage

Doses are population estimates that vary widely between individuals.

Threshold~1 mg
Light1-3 mg
Moderate3-5 mg
Strong5-7 mg
Heavy7+ mg

Duration

Onset5-20 minutes
After Effects1-8 hours
Total1-4 hours

Subjective Effects

Legacy content. A statistically backed ontology from Mindstate Design Labs is coming soon.

The experience is that of a potent, short-acting opioid, dominated by sedation, pain relief, and a relaxed, mood-lifted state. Notably, many users find its euphoria muted relative to typical recreational opioids, a quality it shares with fentanyl. The margin between an active dose and dangerous respiratory depression is narrow, and heavy doses readily progress into somnolence and unconsciousness.

Physical

A heavy, relaxed body state with pronounced pain relief is central to the experience. This is accompanied by the standard opioid side-effect profile of itchiness, nausea, constipation, dry mouth, and constricted pupils, with dose-dependent respiratory depression as the principal danger.

Bodily

Pupil constrictionConstipation

Sedation

Sedation is a core component, scaling from drowsiness and somnolence through fatigue and weakness into unconsciousness at heavy doses.

Cognitive

The headspace is relaxed, dulled, and content, with slowed attention and reduced mental clarity. Confusion, changes in focus, and occasional nervousness or anxiety are reported alongside the mood lift.

Emotional

Mood lift and relaxation are typical, though the euphoric component is often described as underwhelming.

Suppressions

Confusion

Reagent Testing

Expected colorimetric results for common reagent tests. Colors show reaction change over 1–2 minutes.

Marquis(MQ)
white → orange2
Mecke(ME)
white → yellow2
Mandelin(MD)
yellow2 → blue2
Powered by PROtestkit.eu

Pharmacology

Pharmacodynamics

Acetylfentanyl acts as a μ-opioid receptor agonist2, producing its effects through binding at the same receptor sites engaged by endogenous endorphins. Its high lipophilicity allows it to penetrate the central nervous system more readily than many other opioids, contributing to its potency.citation needed In animal studies using selective antagonists, its activity was confirmed to be mediated primarily through the μ-opioid receptor; a δ-opioid antagonist did not alter its effects, while a μ-opioid antagonist reduced them and naltrexone fully reversed them. Acetylfentanyl has been estimated to be approximately 15 times more potent than morphine as an analgesic (with an ED50 of 0.021 mg/kg in the mouse acetic acid writhing test) and roughly 15 times less potent than fentanyl.

Pharmacokinetics

Acetylfentanyl's high lipophilicity, its ability to dissolve in fats and lipids, allows it to penetrate the central nervous system more readily than many other opioids, contributing to its potency relative to morphine. The metabolism of Acetylfentanyl has been documented, Metabolites were formed via N-dealkylation, followed by hydroxylation, monohydroxylation preferably at the ethyl linker, followed by glucuronidation or sulfation, monohydroxylation and carbonylation, dihydrodiol formation, dihydroxylation with methylation at the phenyl ring as well as amide hydrolysis.citation needed

Metabolitesnone documented yet

Interactions

Dangerous

Highest risk

These combinations are considered extremely harmful and should always be avoided. Reactions to these drugs taken in combination are highly unpredictable and have a potential to cause death.

AlcoholBenzodiazepinesCocaineDXMGHB/GBLKetamineMXEPregabalinTramadol

Unsafe

Avoid

There is considerable risk of physical harm when taking these combinations, they should be avoided where possible.

Caution

Use caution

These combinations are not usually physically harmful, but may produce undesirable effects, such as physical discomfort or overstimulation. Extreme use may cause physical health issues. Synergistic effects may be unpredictable. Care should be taken when choosing to use this combination.

AmphetaminesMAOIsMephedroneNitrous oxidePCP
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Tolerance

Tolerance timelines are rules of thumb, not exact schedules, and vary widely between individuals and use patterns.

Full Tolerance
Repeated acetylfentanyl use over time can lead to tolerance for many effects. The pace differs by effect, with constipation-related tolerance developing especially slowly relative to other opioid effects. Because of this uneven tolerance pattern, users may need progressively larger doses to obtain the same subjective effects.
Baseline Reset
1-2 weeks
Half Tolerance
3-7 days
Cross Tolerance

Opioids (all classes)

Harm Potential

Addiction & Dependence

Psychological

High

Acetylfentanyl presents an extremely high risk of addiction and abuse, and its use can lead to psychological dependence.citation needed Compulsive redosing is commonly reported, especially because its effects are short-lived.

Physical

Extremely High

Chronic use leads to extreme physical dependence. Cravings and withdrawal symptoms occur upon sudden cessation. Animal studies have demonstrated that acetylfentanyl can completely suppress morphine withdrawal symptoms, confirming significant cross-dependence liability with other opioids.

Toxicity

Gastrointestinal

Animal toxicity studies observed significant bleeding in the small intestines of mice administered acetylfentanyl; the relevance of this finding to human use at typical doses remains unclear.

Respiratory

Respiratory depression occurs at doses proportionally closer to the psychoactive range than with many other opioids; this effect can rapidly progress to fatal anoxia, with pulmonary edema documented in overdose fatalities.citation needed

History & Culture

Discovery and Early History

Acetylfentanyl was first described in patents from Research Laboratorium Dr. C. Janssen (Janssen Pharmaceutica), a Belgian pharmaceutical company. Its analgesic activity was characterized in a 1968 patent by Paul Janssen, the company's founder. The compound was discovered contemporaneously with

Legality

International

1961 Single Convention: acetylfentanyl is controlled in Schedules I and IV.

1971 Convention on Psychotropic Substances: acetylfentanyl is not scheduled.

1988 Convention: acetylfentanyl is not listed in precursor Tables I or II.

By Country

Illegal18
United States flagUnited StatesIllegal
Austria flagAustriaIllegal
Canada flagCanadaIllegal
Cyprus flagCyprusIllegal (analog/blanket ban)
Estonia flagEstoniaIllegal
Finland flagFinlandIllegal
Germany flagGermanyIllegal
Ireland flagIrelandIllegal (analog/blanket ban)
Japan flagJapanIllegal
Latvia flagLatviaIllegal
Lithuania flagLithuaniaIllegal
Norway flagNorwayIllegal
Poland flagPolandIllegal
Russia flagRussiaIllegal
Sweden flagSwedenIllegal
Switzerland flagSwitzerlandIllegal
Turkey flagTurkeyIllegal
United Kingdom flagUnited KingdomIllegal
Not scheduled1
China flagChinaCategory I Psychotropic Substance

References

Source Pages

  1. DanceSafe: Fentanyl Information
  2. Erowid
  3. Erowid: Acetylfentanyl Vault
  4. Isomer Design (TiHKAL/PiHKAL)
  5. PsychonautWiki
  6. The Drug Classroom
  7. TripSit Factsheets
  8. TripSit Wiki
  9. TripSit: Drug Combinations Chart
  10. TripSit: Drug Combinations Wiki
  11. Wikipedia

Citations

  1. Mohr ALA, Friscia M, Papsun D, Kacinko SL, Buzby D, & Logan BK. (2016). Acetyl Fentanyl, a Novel Fentanyl Analog, Causes 14 Overdose Deaths in Rhode Island, March–May 2013. Journal of Analytical Toxicology. https://pmc.ncbi.nlm.nih.gov/articles/PMC4469714/1
  2. European Monitoring Centre for Drugs Drug Addiction, & European Police Office. (June 2016). EMCDDA–Europol Joint Report on acetylfentanyl. European Monitoring Centre for Drugs and Drug Addiction (EMCDDA). https://doi.org/10.2810/8906941
  3. Schedules of Controlled Substances: Temporary Placement of Acetyl Fentanyl Into Schedule I. Drug Enforcement Administration / Federal Register (2015). https://www.govinfo.gov/content/pkg/FR-2015-07-17/html/2015-17563.htm1
  4. Suchtgiftverordnung, Annex I, I.1.b (RIS consolidated federal law). ris.bka.gv.at (n.d.). https://ris.bka.gv.at/normdokument.wxe?abfrage=bundesnormen&anlage=1&gesetzesnummer=100110531
  5. Controlled Drugs and Substances Act, Schedule I. laws-lois.justice.gc.ca (n.d.). https://laws-lois.justice.gc.ca/eng/acts/C-38.8/page-17.html1
  6. Controlling Fentanyl-Related Substances – China's Contribution (White Paper). People's Republic of China / Consulate General (2025). https://erbil.china-consulate.gov.cn/eng/zgxw/202503/t20250305_11568662.htm1
  7. K.D.P. 367/2025 — Narcotic Drugs and Psychotropic Substances (Controlled Drugs) (Amendment) Order 2025. cylaw.org (n.d.). https://www.cylaw.org/KDP/data/2025_1_367.pdf1
  8. CyLaw 2025 Gazette index. cylaw.org (n.d.). https://www.cylaw.org/KDP/2025.html1
  9. Narcotic Drugs and Psychotropic Substances Law 29/1977 (consolidated text). cylaw.org (n.d.). https://www.cylaw.org/nomoi/enop/non-ind/1977_1_29/full.html1
  10. Acetyl Fentanyl — Drug and Chemical Evaluation Section identity sheet. deadiversion.usdoj.gov (n.d.). https://www.deadiversion.usdoj.gov/drug_chem_info/acetylfentanyl.pdf1

Further Reading

  1. ChemSpider: Acetylfentanyl
  2. Fentanyl and its derivatives: Pain-killers or man-killers? (Heliyon 2024)

Article Status

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