4-AcO-MET
4-acetoxy-N-methyl-N-ethyltryptamine
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4-AcO-MET (4-acetoxy-N-methyl-N-ethyltryptamine) — metacetin — is a synthetic psychedelic of the tryptamine class. It is a prodrug of 4-HO-MET, a close structural analog of psilocin. It activates serotonin receptors in the brain, producing the visual and cognitive shifts characteristic of classical psychedelics.[1]
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psilocybin, psilocin, LSD +4 morepsilocybin, psilocin, LSD, DMT, mescaline, 4-AcO-DMT, 4-HO-MiPT show less
The active metabolite 4-HO-MET was first synthesized by Alexander Shulgin in the early 1970s and formally described in TiHKAL in 1997.[2][3] The acetate ester prodrug appeared on the European research chemical market in 2009, sold as a legal substitute for controlled psilocin analogs.[4] No clinical trials have been registered in any jurisdiction, and it remains a research chemical with no approved medical use.
Subjective effects include geometric visual patterns, color enhancement, time alteration, elevated mood, and heightened emotional sensitivity. The experience is warm and visually rich — lighter than psilocybin, with a playful, aesthetic character that favors immersion over introspection. Nausea during onset, thought loops, and acute anxiety in unsupported settings are common unwanted effects.
4-AcO-MET produces no physical dependence, and no lethal dose has been established in any species.[5] The primary risks are psychological — panic, prolonged distress, or psychotic episodes — amplified by combining with MAOIs or tramadol, which can trigger a life-threatening serotonin overload.[6] No clinical studies exist; what is known comes from structural analogy to psilocin, laboratory binding data, and uncontrolled self-reports.[7]
History[edit]
Discovery
4-HO-MET was synthesized by Alexander Shulgin in the early 1970s. He described it in TiHKAL in 1997, reporting effects so similar to psilocin that he doubted the two could be distinguished in blinded testing.[2][3] The acetate ester prodrug 4-AcO-MET was not described in Shulgin's published work.
Novel psychoactive substance era
4-AcO-MET appeared on the European research chemical market in 2009, distributed almost exclusively as the fumarate salt.[4] It arrived alongside a wave of 4-acetoxy tryptamines marketed as legal alternatives to controlled psilocin analogs. Its crystal structure was confirmed by X-ray diffraction in 2021,[8] and 4-HO-MET was identified in seized drug samples by Chinese forensic laboratories.[9]
Present status
No clinical trials have been registered for 4-AcO-MET in any jurisdiction as of April 2026. Pharmacological data come primarily from in vitro binding studies and structural analogy to psilocybin.
The name metacetin follows the informal naming convention for 4-substituted tryptamines — paralleling psilocin (4-HO-DMT), psilacetin (4-AcO-DMT), and metocin (4-HO-MET). In research chemical communities, 4-AcO-MET is sometimes described as a lighter or more visual alternative to psilocybin mushrooms — a reputation based on uncontrolled self-reports rather than comparative studies.
Chemistry[edit]
4-AcO-MET belongs to the 4-substituted tryptamine family — the same chemical class as psilocin and 4-AcO-DMT. Its molecular formula is C₁₅H₂₀N₂O₂ (260.33 g/mol), and its crystal structure was confirmed by X-ray diffraction in 2021.[8]
It is the acetate ester of 4-HO-MET — the body converts it to 4-HO-MET after ingestion, making 4-HO-MET the active compound.
Pharmacology[edit]
Mechanism of action
4-AcO-MET is a prodrug. After ingestion, the body converts it to 4-HO-MET — the compound responsible for its effects.[10] 4-HO-MET activates serotonin receptors in the brain, producing the perceptual and cognitive shifts of classical psychedelics.[1][7]
Pharmacokinetics
No human pharmacokinetic data have been published for 4-AcO-MET. Based on closely related compounds, the body first breaks down the ester bond to release 4-HO-MET, then processes it further through the liver.[10][11] Shulgin reported a duration of 4–6 hours for the active metabolite — consistent with other psilocin-class tryptamines.[2]
Neuroscience[edit]
Where it acts
No neuroimaging studies of 4-AcO-MET or 4-HO-MET have been published. As a psilocin-class compound, it is expected to activate specific neurons in the prefrontal cortex — the same trigger identified in psilocybin research. This disrupts the brain's default network, loosens sensory filtering, and increases connections between normally separate regions.
Why it matters
One influential framework suggests psychedelics reduce the brain's confidence in its existing assumptions, letting raw sensory input take more control. The visual distortions, unusual thoughts, and ego dissolution reported with 4-AcO-MET fit this picture. Psilocin-class tryptamines may also promote new brain connections,citation needed but this has not been confirmed for 4-HO-MET at human doses.
- Does 4-HO-MET produce the same pattern of default mode network disruption observed with psilocin, or does the N-methyl-N-ethyl substitution alter regional brain activation?
- Does the intact prodrug 4-AcO-MET have any direct brain activity before conversion to 4-HO-MET?
- How do differences in non-serotonergic binding across the N,N-dialkyl tryptamine series[12] translate to differences in subjective experience?
Subjective Effects[edit]
The 4-AcO-MET experience is warm, visually generous, and emotionally open. Colors shift and brighten, surfaces acquire a living quality, and mood rises quickly. The tone is playful rather than solemn — it draws toward aesthetic immersion and sensory engagement rather than psychological excavation.[3]
Community reports place 4-AcO-MET closest to psilocybin and 4-AcO-DMT in character. Shulgin considered 4-HO-MET effectively indistinguishable from psilocin in blinded testing.[3] Many users describe a more visual and less introspective quality compared with psilocybin at equivalent doses, though this has not been formally verified.
Effect Grid
At common doses (20–30 mg oral), the full psychedelic experience develops. Visual effects become pronounced: geometric patterning overlays surfaces, colour enhancement intensifies, environmental objects may drift, morph, or breathe rhythmically. Closed-eye visuals feature complex geometric imagery. Time distortion is significant — minutes may feel expanded or compressed unpredictably.
Thought acceleration and conceptual thinking increase substantially. Emotional responses to stimuli — music, nature, interpersonal interaction — can feel profoundly meaningful. Ego softening may begin, with the boundary between self and environment becoming less distinct. Thought loops are possible.
Body load is moderate: nausea during come-up, jaw tension, temperature fluctuation, and difficulty with fine motor tasks are common. Sleep is not possible during the active phase. Total commitment is 5–6 hours including afterglow.
Modeled from the effect's dose-dependence curve — not per-substance measurements.
Geometry · Visual breathing · Symmetrical texture repetition · After-images · Environmental patterning · Auditory enhancement · Brightness alteration · Visual morphing · Sound sensitivity · Auditory distortion · Depth perception distortion · Light sensitivity · Peripheral vision distortion · Perspective distortion · Proprioceptive distortion · Visual diffraction · Visual haze / noise · Visual acuity enhancement · Spatial disorientation · Auditory misinterpretation · Peripheral misidentification · Touch enhancement · Vestibular distortion · Visual melting · Synesthesia · Internal hallucinations · Object transformations · Visual recursion · Object activation · External hallucinations · Visual scenery slicing · Auditory hallucinations · Perspective hallucinations · Olfactory hallucination
Environmental patterning · Auditory enhancement · Brightness alteration · Visual morphing · Sound sensitivity · Auditory distortion · Depth perception distortion · Light sensitivity · Peripheral vision distortion · Perspective distortion · Proprioceptive distortion · Visual diffraction · Visual haze / noise · Visual acuity enhancement · Spatial disorientation · Auditory misinterpretation · Peripheral misidentification · Touch enhancement · Vestibular distortion · Visual melting · Synesthesia · Internal hallucinations · Object transformations · Visual recursion · Object activation · External hallucinations · Visual scenery slicing · Auditory hallucinations · Perspective hallucinations · Olfactory hallucination
Wakefulness · Appetite suppression · Heart rate perception changes · Insomnia · Laughter fits · Tingling / electric sensations · Vibrations / buzzing · Nausea · Body schema distortion · Bodily lightness · Dizziness · Dry mouth · Physical fatigue · Restlessness · Tactile euphoria · Muscle relaxation · Muscle tension · Bodily heaviness · Headache · Yawning · Sedation · Watery eyes · Nasal congestion · Salivation · Bruxism · Brain zaps · Bodily dissociation
Laughter fits · Tingling / electric sensations · Vibrations / buzzing · Nausea · Body schema distortion · Bodily lightness · Dizziness · Dry mouth · Physical fatigue · Restlessness · Tactile euphoria · Muscle relaxation · Muscle tension · Bodily heaviness · Headache · Yawning · Sedation · Watery eyes · Nasal congestion · Salivation · Bruxism · Brain zaps · Bodily dissociation
Pattern recognition enhancement · Conceptual thinking · Immersion enhancement · Thought connectivity · Cognitive euphoria · Cognitive flexibility · Cognitive impairment · Openness enhancement · Memory suppression · Thought acceleration · Focus suppression · Increased nature relatedness · Multiple thought streams · Creativity enhancement · Humor enhancement · Thought loops · Synchronicity · Analysis enhancement · Thought disorganization · Confusion · Memory fragmentation · Focus enhancement · Cognitive dysphoria · Delusions
Thought connectivity · Cognitive euphoria · Cognitive flexibility · Cognitive impairment · Openness enhancement · Memory suppression · Thought acceleration · Focus suppression · Increased nature relatedness · Multiple thought streams · Creativity enhancement · Humor enhancement · Thought loops · Synchronicity · Analysis enhancement · Thought disorganization · Confusion · Memory fragmentation · Focus enhancement · Cognitive dysphoria
Simultaneous emotions · Anxiety · Catharsis · Anxiety suppression · Dysphoria
Dysphoria
Sociability enhancement · Depersonalization · Boundary dissolution · Ego dissolution · Identity alteration
Identity alteration
Timeline
First alerts appear as a subtle shift in body awareness — mild stomach butterflies, slight visual brightening, or a gentle change in headspace. Effects are easily mistaken for placebo at the lower end of this window.
Perceptual intensity builds steadily. Colours saturate, surfaces begin to drift or breathe, and a distinct cognitive shift becomes undeniable. Nausea peaks during this phase for most individuals.
Maximum visual, cognitive, and emotional intensity. Geometric patterning, colour enhancement, and environmental distortion are at their strongest. Thought connectivity and emotional depth reach their zenith.
Intensity diminishes from peak but remains clearly psychedelic. Visual effects soften to gentle drifting and colour warmth. Cognitive clarity gradually returns, often accompanied by a reflective, introspective quality.
Effects recede toward baseline. Mild visual trails and enhanced colour perception may linger. Mental state shifts toward calm lucidity.
Residual mood elevation, enhanced emotional openness, and mild visual sensitivity persist after the primary experience resolves. Some individuals report improved sleep quality; others experience mild residual stimulation.
⚠ Do not drive or operate heavy machinery for the remainder of the day following use, as subtle perceptual and cognitive effects may persist below conscious awareness.
Safety[edit]
- Acute toxicity
- Low
- Chronic toxicity
- Negligible
- Withdrawal
- None
- Tolerance buildup
- rapid
- Tolerance reset
- 7 days
- Physical
- None
- Psychological
- Negligible
- Compulsive redosing
- Negligible
- Dose escalation
- Negligible
- Cross-tol.
- psilo · psilocin · LSD
Toxicity
No lethal dose has been established for 4-AcO-MET or 4-HO-MET in any species, and no controlled toxicity studies have been conducted.
Computer modelling of the close structural analog 4-AcO-DMT predicts moderate-to-high acute toxicity, with the heart and gastrointestinal tract as primary predicted target organs.[13] No mutagenic or endocrine-disrupting activity was predicted.[13] These predictions derive from a structural analog and cannot serve as a safety threshold for 4-AcO-MET.
Cardiovascular considerations
The 4-hydroxylated tryptamine class shows relatively weak activity at the serotonin receptor associated with heart valve damage.[1] This suggests lower valvulopathy risk compared with potent agonists at that receptor, though the clinical relevance for intermittent use remains uncertain.
Forensic toxicology
One death has been reported in which 4-HO-MET was detected in postmortem specimens.[14] The death was attributed to another substance (4-MeO-PCP); 4-HO-MET was not identified as a contributing cause. Novel tryptamines are typically absent from standard toxicology panels, so cases may go undetected.[15] Deaths directly attributable to classical serotonergic psychedelics are rare compared with other drug classes.[16]
Psychological risks
No controlled studies have evaluated psychological adverse effects of 4-AcO-MET specifically. Class-level data indicate that a small proportion of people reporting difficult psychedelic experiences have functional impairment lasting more than a day, and some seek professional help.citation needed
Risk factors for severe adverse experiences include high doses, a negative mental state at onset, lack of social support, and co-use of lithium or mood stabilizers. Persistent visual disturbances after psychedelic use — a condition called HPPD — have been documented across the serotonergic psychedelic class[5] but not specifically for 4-AcO-MET. Adverse events are uncommon in controlled settings but substantially more likely with uncontrolled use.[5]
Tolerance and dependence
A single dose builds rapid tolerance — effects diminish sharply with repeated dosing within a day.[17] This tolerance extends to all classical serotonergic psychedelics and resets within approximately 7 days.[17] Classical serotonergic psychedelics have low abuse liability, and no withdrawal has been described for any member of this class.[5]
Drug interactions
Serotonergic combinations
The primary pharmacological risk in combination is serotonin syndrome — a dangerous condition caused by excessive serotonergic activity that can produce overheating, muscle rigidity, and seizures.
MAOIs: Monoamine oxidase inhibitors block the primary breakdown pathway for tryptamines, dramatically raising drug levels in the body. Serotonin syndrome risk is high. This combination is contraindicated for all serotonin 2A receptor agonist tryptamines.[6]
SSRIs/SNRIs: Chronic SSRI use may reduce psychedelic effects by downregulating serotonin receptors. At high doses, concurrent use carries potential serotonin syndrome risk.[6]
Seizure threshold interactions
Lithium: Co-administration with serotonergic psychedelics has been associated with seizures and cardiovascular complications.[6] This is a serious risk.
Cannabis
No published interaction data exist. Anecdotal reports suggest THC can intensify psychedelic effects, particularly in the visual and time-distortion domains.
Contraindications
Contraindication data are inferred from psilocybin class-level pharmacology.[6]
Absolute contraindications:
- Personal or family history of psychotic disorders: serotonin receptor activation may precipitate or worsen psychotic episodes.
- Concurrent lithium use: seizure and cardiovascular risk.
- Concurrent MAOI use: serotonin syndrome risk.
Relative contraindications:
- Bipolar disorder: risk of manic episode precipitation.
- Concurrent SSRI/SNRI use: unpredictable effect modulation and serotonin syndrome risk at high doses.
- Concurrent tramadol use: serotonin syndrome and seizure risk.
- Pregnancy: no reproductive safety data exist for any 4-substituted tryptamine.
- Cardiovascular conditions: transient increases in heart rate and blood pressure are expected.
Harm Reduction[edit]
Forms & Identification
4-AcO-MET is almost exclusively sold as the fumarate salt — a white to off-white crystalline powder visually indistinguishable from dozens of other research chemical powders. Reagent testing is the only reliable way to confirm identity and rule out substitution. An analytical milligram scale (±1 mg) is essential; differences of a few milligrams can shift the experience significantly.
Guidelines
- Test the substance with at least two reagent kits before use.
- Weigh every dose on a milligram-precision scale — never estimate powder by eye.
- Start at the low end of the dose range for first experiences.
- Choose a safe, comfortable setting with at least one sober person present.
- Have no obligations for the following 8–10 hours; do not drive.
- Eat lightly 2–3 hours beforehand to reduce nausea.
- Keep water accessible; stay hydrated without overdrinking.
- If effects feel too intense, change the physical environment — a shift in sensory input can redirect the experience.
- Do not redose within the first 90 minutes; onset can be slow and unpredictable.
Set & Setting
Psychedelic response is highly sensitive to psychological state and physical environment. A calm, familiar space with trusted company is the most reliable way to reduce the likelihood of a difficult experience. First-time users benefit from a sober companion who can provide reassurance without intervention.
Avoid using when anxious, grieving, or in unfamiliar social situations — these conditions are the primary predictors of challenging experiences across the psychedelic class.
Aftercare & integration. The days following a psychedelic experience are a window for reflection. Journaling while impressions are fresh — even fragmentary notes — helps consolidate insight before it fades. Discuss the experience with a trusted person or, for difficult sessions, a therapist experienced with psychedelic integration.
Expect mild fatigue and emotional sensitivity for 24–48 hours. Prioritize sleep, light nutrition, and low-demand activities. If distressing thoughts or perceptual changes persist beyond a week, seek professional support — early intervention improves outcomes.
Recovery & Support
Classical psychedelics have low abuse liability, and compulsive use patterns are uncommon. When problematic use does develop, it typically reflects underlying psychological distress rather than pharmacological dependence.
If psychedelic use is causing distress, interfering with daily function, or being used to avoid facing difficult emotions, support is available through harm reduction organizations and psychedelic integration therapists. No specialized detoxification is required.
Recovery resources, crisis lines, and support pathways → View all
Emergency Response
Recognizing an emergency: Most difficult psychedelic experiences are uncomfortable but not medically dangerous. Seek immediate help if someone shows signs of self-harm intent, complete disconnection from reality (unable to recognise people or surroundings), seizures, severe chest pain, or loss of consciousness.
Immediate steps:
- Stay with the person. Speak calmly and simply.
- Move them to a quiet, low-stimulation environment if possible.
- Do not physically restrain unless there is immediate danger of self-harm or harm to others.
- If the person is unconscious, place them in the recovery position.
- Call emergency services if symptoms escalate or the situation is unclear.
What to tell the dispatcher: Name the substance (4-AcO-MET), approximate amount taken, time of ingestion, and current symptoms. Good Samaritan laws in many jurisdictions protect callers who report drug-related emergencies — do not let fear of legal consequences delay the call.
Legal Status[edit]
As of April 2026, 4-AcO-MET has a fragmented legal status internationally — not specifically scheduled in some jurisdictions, but covered by catch-all provisions, structural analog statutes, or prodrug reasoning in many others.[4]
| Jurisdiction | Classification | Key provisions |
|---|---|---|
| United States | Not specifically scheduled (CSA) | The Federal Analogue Act may apply if intended for human consumption, as 4-AcO-MET is a structural analog of psilocin (Schedule I). |
| United Kingdom | Class A (Misuse of Drugs Act 1971) | Controlled as an ester of 4-HO-MET under the tryptamine catch-all clause. |
| Germany | Controlled (NpSG) | Listed under the Neue-psychoaktive-Stoffe-Gesetz. Sale, purchase, and production are prohibited; personal possession is not penalized under NpSG. |
| Switzerland | Controlled (Verzeichnis E) | Listed under the Swiss Federal Act on Narcotics since at least 2019. |
| Canada | Not controlled | Not listed in the Schedule to the Controlled Drugs and Substances Act as of 2025. |
| Australia | Likely Schedule 9 (unconfirmed) | Not specifically listed. Analog reasoning suggests Schedule 9 classification, but no primary legislative confirmation was identified.citation needed |
Analog and prodrug considerations
In the United States, the Federal Analogue Act (21 U.S.C. § 813) treats substances substantially similar to Schedule I or II compounds as controlled if intended for human consumption. 4-AcO-MET is structurally similar to psilocin and converts to 4-HO-MET — a psilocin analog — in the body, creating substantial prosecutorial basis even without a specific listing.
In the United Kingdom, the Misuse of Drugs Act 1971 explicitly covers esters of controlled tryptamines, making the Class A classification unambiguous.
references
- [1] ^abcMcKenna DJ, Repke DB, Lo L, Peroutka SJ (1990) Differential interactions of indolealkylamines with 5-hydroxytryptamine receptor subtypes — Neuropharmacology PMID:2139186
- [2]
- [3]
- [4]
- [5] ^abcdSchlag AK, Aday J, Salam I, Neill JC, Nutt DJ (2022) Adverse effects of psychedelics: From anecdotes and misinformation to systematic science — Journal of Psychopharmacology doi:10.1177/02698811211069100
- [6]