WARNINGDANGER OF DEATH
High doses alone or ordinary doses in combination with other depressants can fatally stop breathing.
Acetylfentanyl
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.
Duration
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.
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
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
Dangerous
Highest riskThese 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.
Unsafe
AvoidThere is considerable risk of physical harm when taking these combinations, they should be avoided where possible.
Caution
Use cautionThese 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.
Tolerance
Tolerance timelines are rules of thumb, not exact schedules, and vary widely between individuals and use patterns.
Opioids (all classes)
Harm Potential
Addiction & Dependence
Psychological
HighAcetylfentanyl 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 HighChronic 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
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 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
References
Source Pages
Citations
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- CyLaw 2025 Gazette index. cylaw.org (n.d.). https://www.cylaw.org/KDP/2025.html1
- 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
- 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
Article Status
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