5-APB
5-(2-aminopropyl)benzofuran
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5-APB (5-(2-aminopropyl)benzofuran) — Benzofury — is a synthetic entactogen-stimulant of the benzofuran class. It is a close structural analog of MDA, distinguished by stronger psychedelic character than MDMA.[1][2] 5-APB is a monoamine releasing agent and serotonin 2A receptor agonist, producing its effects by reversing serotonin transporters while directly activating serotonin receptors.[3]
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MDMA, MDA, 6-APB +2 moreMDMA, MDA, 6-APB, 5-MAPB, 6-MAPB show less
Synthesized circa 1993 by David Nichols as a potential non-neurotoxic alternative to MDMA,[4] 5-APB remained a laboratory curiosity for over a decade. It entered recreational markets in 2010 under the brand name "Benzofury," prompting rapid scheduling in the United Kingdom and Germany. No clinical trials have been registered, and it circulates primarily through unregulated markets.
Subjective effects include cognitive euphoria, empathogenic warmth, sensory enhancement, and mild geometric visual patterns. The experience sits between entactogen and psychedelic — warmer and more social than a classical psychedelic, but more perceptually active than MDMA, with a character closer to MDA. Nausea, jaw tension, anxiety during the comedown, and a multi-day recovery period of low mood are common unsought effects.
Dependence liability is moderate and comparable to MDMA, while the toxic dose remains poorly defined — two fatalities bracket post-mortem blood concentrations between 0.86 and 5.6 mg/L.[5][6] The primary chronic risk is cardiac valve damage driven by potent 5-HT₂B receptor activation,[7][2] compounded by a triple serotonergic mechanism — monoamine release, MAO-A inhibition, and direct receptor agonism — that creates an unusually steep serotonin syndrome curve.[3] No controlled human studies exist; the current understanding rests on in vitro pharmacology, animal data, and case reports.
History[edit]
Discovery
5-APB was first synthesized circa 1993 by David Nichols at Purdue University as part of a programme investigating non-neurotoxic alternatives to MDMA.[4] The strategy replaced the methylenedioxy ring of MDA with a benzofuran oxygen, aiming to preserve entactogenic activity while reducing serotonergic neurotoxicity. A patent covering 5-APB and 6-APB was filed circa 2000 by researchers at Eli Lilly, investigating these compounds as potential 5-HT₂C agonists.[4]citation needed
Market emergence
5-APB appeared on the research chemical market in 2010, detected by the European Monitoring Centre for Drugs and Drug Addiction.[4] Sold alongside its isomer 6-APB under the brand name "Benzofury," it was marketed as a legal alternative to MDMA, predominantly in the United Kingdom.[8] Products under this label frequently contained variable and undisclosed substances, complicating attribution of specific effects or adverse events to 5-APB alone.[8]
Prohibition and current status
The UK issued a Temporary Class Drug Order covering 5-APB and related benzofurans on 10 June 2013,[9] permanently classifying it as Class B one year later.[8] Germany added it to Anlage II of the BtMG in July 2013.[4] The first published fatality appeared in 2014,[6] and the definitive in vitro pharmacological profile was established by Rickli et al. in 2015.[2]
The name "Benzofury" — a portmanteau of benzofuran and fury — became the dominant market identity for the entire aminoalkylbenzofuran family during 2010–2013. In practice, the label covered multiple compounds (5-APB, 6-APB, 5-MAPB, 6-MAPB) sold interchangeably, making "Benzofury" more brand than substance identifier. This naming ambiguity persists in harm reduction discussions, where users sometimes conflate the pharmacologically distinct isomers.
Chemistry[edit]
Structural class
5-APB belongs to the aminoalkylbenzofuran class of phenethylamine derivatives. The parent scaffold is amphetamine, with a benzofuran oxygen replacing one carbon of the methylenedioxy bridge found in MDA. The "5" designation indicates substitution at the 5-position of the benzofuran ring, distinguishing it from 6-APB, where the chain attaches at the 6-position — a positional difference that produces measurably different pharmacological and toxicological profiles despite identical molecular formulae.
Related compounds include 5-MAPB (the N-methyl derivative, structurally analogous to MDMA as 5-APB is to MDA), 6-APB, and 6-MAPB.
Molecular properties
| Molecular formula | C₁₁H₁₃NO |
| Molecular weight | 175.23 g/mol |
The molecule comprises a benzofuran bicyclic system bearing a 2-aminopropyl chain at the 5-position.[10] Its molecular weight (175.23 g/mol) is slightly lower than MDA (179.22 g/mol), reflecting the replacement of the methylenedioxy CH₂ bridge with a single oxygen atom.
Stereochemistry
5-APB possesses one chirality centre at the α-carbon of the aminopropyl side chain. Commercially available material is racemic mixture.[10] No published studies have investigated differential activity of the (R)- versus (S)-enantiomers. By analogy with MDA — where the (R)-enantiomer is the more potent SERT substrate — enantiospecific activity differences are plausible but unconfirmed.
Physical properties
No published characterization of melting point, boiling point, aqueous solubility, or storage stability has been identified for 5-APB in either free base or salt form.
Pharmacology[edit]
Mechanism of action
5-APB is a monoamine releasing agent — it reverses the transporters for serotonin (SERT), dopamine (DAT), and norepinephrine (NET), causing these neurotransmitters to flood into the synaptic cleft rather than simply blocking their reuptake.[2][1] This mechanism is shared with MDMA and MDA.
Beyond transporter reversal, 5-APB directly activates 5-HT₂A, 5-HT₂B, and 5-HT₂C receptors with greater potency than MDMA at all three.[3] It is also a potent MAO-A inhibitor,[3] meaning it blocks the enzyme responsible for breaking down serotonin after release.
This triple serotonergic mechanism — transporter reversal, receptor activation, and enzyme inhibition — is unusual among recreational entactogens. It places 5-APB pharmacologically closer to MDA than to MDMA, as confirmed by microdialysis in rats.[1]
At recreational concentrations, 5-APB also engages dopamine receptors, adrenergic receptors, and nicotinic acetylcholine receptors,[11] contributing to its stimulant and cardiovascular effects.
Pharmacokinetics
No controlled human pharmacokinetic studies have been published for 5-APB. The closest structural analog with human data is 5-MAPB, which showed a half-life of approximately 6.5 hours in a clinical case — comparable to MDMA.[12] As a structurally different compound (secondary versus tertiary amine), the actual half-life of 5-APB may differ.
5-APB is itself a metabolite of 5-MAPB, formed when the body removes the N-methyl group.[13][14] Its own metabolism likely involves the same liver enzymes documented for the 6-isomer series,[15] though this has not been directly confirmed.
A critical finding is that liver metabolism of 5-APB generates toxic reactive intermediates rather than simply clearing the drug — blocking the responsible enzyme (CYP3A4) reduced liver cell damage in laboratory models.[16]
Oral bioavailability, peak blood concentration, and time to peak have not been characterized in any species.
Neuroscience[edit]
Where it acts
No neuroimaging data exist for 5-APB in humans. Based on its pharmacological profile, 5-APB is expected to modulate the same neural circuits as MDMA and MDA: serotonin release dampens amygdala fear reactivity and enhances prefrontal-amygdala connectivity — the neural basis of entactogenic warmth and emotional openness — while dopamine release activates mesolimbic reward circuitry[17] and norepinephrine release drives sympathetic arousal.
The stronger 5-HT₂A agonism relative to MDMA[3] predicts greater activation of cortical pyramidal neurons, the cellular trigger for psychedelic-like perceptual effects — consistent with 5-APB's MDA-like character.
Why it matters
5-APB sits at the intersection of reward (dopaminergic "wanting") and hedonia (serotonergic "liking"), with its serotonin-preferring ratio predicting stronger empathogenic effects than pure stimulants while retaining moderate mesolimbic pathway activation.[18][17] Its pharmacological overlap with MDMA's therapeutic mechanism — facilitated fear memory processing under reduced amygdala reactivity — motivated its inclusion in screening panels for potential anti-PTSD compounds.[3]
Key unknowns include whether 5-APB promotes neuroplasticity as MDMA does via BDNF expression, whether its MAO-A inhibition is reversible or persists beyond the acute experience (extending the interaction risk window), and whether chronic use produces detectable heart valve damage — the highest-priority translational question given the compound's potent 5-HT₂B agonism.
Subjective Effects[edit]
5-APB produces an experience that blends entactogenic warmth with mild psychedelic character — closer to MDA than to MDMA in feel. Empathogenic openness and sensory enhancement dominate in social settings; introspective depth and perceptual shifts become more prominent alone or in quiet environments. The experience intensifies across the dose range from gentle mood lift and sociability toward pronounced visual and cognitive alteration at higher doses.
Compared to MDMA, 5-APB is reported as more stimulating and longer-lasting with greater perceptual distortion, consistent with its elevated 5-HT₂A activity. Relative to 6-APB, user reports suggest a broadly similar entactogenic character, though systematic comparison data are lacking.
Effect Grid
At common doses (approximately 50–80 mg oral), the full entactogenic experience manifests. Empathy enhancement is prominent — emotional barriers diminish, and interpersonal connection feels deeply facilitated. Cognitive euphoria is strong and sustained. Music enhancement reaches its characteristic peak, with complex emotional responses to sound. Sensory perception intensifies across modalities, with colour saturation and tactile sensitivity notably increased.
Physically, stimulation is pronounced: elevated heart rate and blood pressure, excessive sweating, significant jaw clenching, and muscle tension throughout the body. Wakefulness is enforced — sleep is impossible during effects. Appetite is fully suppressed. Nausea may occur during the come-up.
The experience commits approximately 6–8 hours including the come-up, peak, and offset. A comedown phase with cognitive fatigue, irritability, and low mood may follow for 1–3 days.
Modeled from the effect's dose-dependence curve — not per-substance measurements.
Light sensitivity · Sound sensitivity · After-images · Color alteration · Tracers · Visual processing acceleration · Auditory distortion · Geometry · Synesthesia · Visual breathing · Visual drifting
Tracers · Visual processing acceleration · Auditory distortion · Geometry · Synesthesia · Visual breathing · Visual drifting
Pupil dilation · Body scan awareness · Appetite suppression · Spontaneous body sensations · Tactile euphoria · Insomnia · Muscle tension · Bruxism · Dry mouth · Physical fatigue · Excessive sweating · Dehydration sensation · Heart rate perception changes · Laughter fits · Nystagmus (eye wobbles) · Bodily lightness · Restlessness · Tingling / electric sensations · Vibrations / buzzing · Nausea · Sexual arousal suppression · Headache · Dizziness · Trembling · Vomiting · Yawning
Tactile euphoria · Insomnia · Muscle tension · Bruxism · Dry mouth · Physical fatigue · Excessive sweating · Dehydration sensation · Heart rate perception changes · Laughter fits · Nystagmus (eye wobbles) · Bodily lightness · Restlessness · Tingling / electric sensations · Vibrations / buzzing · Nausea · Sexual arousal suppression · Headache · Dizziness · Trembling · Vomiting · Yawning
Introspection enhancement · Thought acceleration · Immersion enhancement · Cognitive fatigue · Novelty enhancement · Motivation enhancement · Humor enhancement · Focus enhancement · Cognitive flexibility · Creativity enhancement · Language enhancement · Thought connectivity · Analysis enhancement · Information processing enhancement · Motivation suppression · Conceptual thinking · Increased nature relatedness · Pattern recognition enhancement · Memory enhancement · Thought organization · Thought deceleration
Novelty enhancement · Motivation enhancement · Humor enhancement · Focus enhancement · Cognitive flexibility · Creativity enhancement · Language enhancement · Thought connectivity · Analysis enhancement · Information processing enhancement · Motivation suppression · Conceptual thinking · Increased nature relatedness · Pattern recognition enhancement · Memory enhancement · Thought organization · Thought deceleration
Anxiety suppression · Catharsis · Irritability · Anhedonia · Anxiety · Emotional lability · Simultaneous emotions · Dysphoria
Anxiety · Emotional lability · Simultaneous emotions · Dysphoria
Sociability enhancement · Emotional susceptibility · Flow state · Craving · Boundary dissolution
Boundary dissolution
Timeline
First alerts emerge as a gentle body warmth and subtle mood lift. Physical awareness increases slightly — a faint tingle or stomach flutter signals absorption.
Stimulation builds noticeably: heart rate rises, jaw tension begins, and sociability increases. Nausea may occur during this phase. Emotional openness starts to emerge.
Full entactogenic plateau with prominent empathy enhancement, cognitive euphoria, and music enhancement. Stimulation is strong — elevated heart rate, sweating, pronounced mydriasis. Emotional depth and sensory richness are at maximum.
Intensity subsides gradually from peak. Entactogenic warmth persists but cognitive sharpness begins to return. Stimulation remains elevated.
Effects recede to a residual stimulation with mild mood elevation. Physical tension eases. Appetite may begin to return.
A comedown lasting 1–3 days characterised by cognitive fatigue, low mood, irritability, and disrupted sleep. Serotonin depletion underlies these residual effects, which are more pronounced after higher doses or repeated use.
⚠ Do not drive or operate machinery until mood and cognitive function have fully returned to baseline — fatigue and impaired concentration may persist for 24–48 hours.
Safety[edit]
- Acute toxicity
- High
- Chronic toxicity
- High
- Withdrawal
- Mild
- Tolerance buildup
- moderate
- Tolerance reset
- 10 days
- Physical
- Low
- Psychological
- Moderate
- Compulsive redosing
- Low
- Dose escalation
- Moderate
- Cross-tol.
- MDMA · MDA · 6-APB
Toxicity
Lethal dose
The toxic dose of 5-APB in humans is unknown. No animal LD₅₀ data specific to 5-APB have been published. Murine data for the closely related 5-MAPB show a narrower safety margin than MDMA: the same dose that killed two-thirds of mice produced no deaths with MDMA.[14]
Two fatal human cases bracket post-mortem blood concentrations:
- 0.86 mg/L — 25-year-old male; 5-APB as primary agent with low-level alcohol and trace THC[5]
- 5.6 mg/L — mixed intoxication with approximately 400 mg 5-APB, approximately 500 mg 3-MMC, and alcohol; cardiovascular collapse approximately four hours after ingestion[6]
A third fatality primarily attributed to other compounds detected 5-APB at 0.546 mg/L, likely as a metabolic product.[19]
Liver damage
5-APB is more toxic to liver cells than its positional isomer 6-APB across all tested laboratory models.[16] The damage occurs through oxidative stress, mitochondrial disruption, and progression from controlled cell death to tissue destruction at higher concentrations. Both 5-APB and 5-MAPB are more hepatotoxic than MDMA in isolated liver cell models.[13]
Liver metabolism through CYP3A4 generates reactive intermediates that contribute to this toxicity — the metabolism itself is part of the problem, not the solution.[16]
Heart damage
5-APB is a potent activator of serotonin₂B receptors at very low concentrations.[7][2] This is the same mechanism responsible for heart valve damage caused by fenfluramine and methysergide — sustained receptor activation causes thickening and scarring of heart valve tissue.[20][2]
Psychological risks
Acute psychological adverse effects include agitation, disorientation, anxiety, panic, confusion, paranoia, and hallucinations at toxic doses.[12][8] A prolonged comedown lasting several days — low mood, irritability, cognitive fatigue — is consistent with serotonin depletion following massive release, the same post-use syndrome observed with MDMA.[8]
No data exist on 5-APB's capacity to trigger persistent psychiatric conditions beyond acute intoxication. The serotonin 2A receptor agonist activity suggests a non-zero risk of HPPD (HPPD), though no cases have been reported.
Tolerance and dependence
No published studies of tolerance development specific to 5-APB exist. Tolerance is expected to follow MDMA-class patterns: acute serotonin depletion reduces the effect of subsequent doses, with recovery dependent on serotonin resynthesis. Community-derived estimates suggest a tolerance half-life of approximately 5 days and full reset within 1.5 weeks.inferred
Cross-tolerance with other serotonin-releasing agents (MDMA, MDA, 6-APB) is expected. Dependence liability is moderate and comparable to MDMA: 5-APB fully substitutes for MDMA in rat drug discrimination studies,[18] and related benzofurans show addictive properties linked to dopamine signaling.[17]
Drug interactions
The combination of serotonin release, MAO-A inhibition,[3] and direct 5-HT₂ receptor activation makes 5-APB one of the more pharmacologically complex entactogens for interaction risk. The acute toxicity pattern documented in case reports — high body temperature, muscle jerking, agitation, confusion — overlaps with the diagnostic criteria for serotonin syndrome.[12]
Serotonergic agents (SSRIs, SNRIs, MAOIs, lithium, triptans, tramadol): The highest-risk interaction class. 5-APB's triple serotonergic mechanism means any additional serotonergic input creates additive or synergistic serotonin elevation. MAOIs are absolutely contraindicated: 5-APB is itself a MAO-A inhibitor, and adding an external MAOI produces compounded monoamine accumulation.[3] Tramadol is flagged as potentially lethal due to combined serotonin effects and seizure threshold reduction.safety citation needed
Alcohol: Present in both documented fatal cases (alcohol levels 0.6–1.4 g/L).[5][6] Alcohol impairs temperature regulation and lowers seizure threshold, compounding 5-APB's acute risks.
Other stimulants: Additive cardiovascular strain — high blood pressure, rapid heart rate, irregular heart rhythm — is expected from co-use with amphetamines, cocaine, or cathinones. The fatal case involving concurrent 3-MMC resulted in cardiovascular collapse.[6]
Contraindications
Heart conditions: Pre-existing valve disease, irregular heart rhythm, or conditions predisposing to cardiac scarring are absolute contraindications given the potent 5-HT₂B activation.[7][2]
Liver disease: 5-APB's demonstrated liver toxicity via metabolic activation[16] makes pre-existing liver impairment an absolute contraindication.
Serotonergic medication: Any ongoing MAOI, SSRI, SNRI, lithium, or triptan therapy contraindicates 5-APB use due to maximal serotonin syndrome risk.
Seizure disorders: Seizures are documented in acute 5-APB intoxication.[6] Pre-existing epilepsy or medications that lower the seizure threshold (tramadol, bupropion) increase risk.
Pregnancy: No reproductive toxicity data exist. By class analogy with amphetamines and MDMA, use during pregnancy is contraindicated.inferred
Harm Reduction[edit]
Forms & Identification
Products sold as 5-APB have historically contained variable substances, particularly during the "Benzofury" era when multiple benzofuran isomers (5-APB, 6-APB, 5-MAPB, 6-MAPB) were sold interchangeably.[8] Reagent testing can distinguish benzofurans from MDMA but cannot reliably differentiate between benzofuran isomers — and the isomers differ meaningfully in toxicity, with 5-APB being more hepatotoxic than 6-APB.[16]
Quantitative laboratory analysis is the only reliable way to confirm isomer identity and purity. Given the compound's uncharacterized dose-response curve, knowing what you have and how much is in it matters more than usual.
Guidelines
- Test your substance. Reagent kits confirm the general class; laboratory analysis confirms the specific isomer. Do not assume a product labeled "5-APB" or "Benzofury" contains only 5-APB.
- Start low. The dose-response curve is uncharacterized. Begin at the lowest reported active dose and wait the full onset period (up to 90 minutes orally) before considering re-assessment.
- Do not redose. The long duration and MAO-A inhibition mean a second dose compounds both serotonergic load and cardiovascular strain disproportionately.
- Stay cool and hydrated. Maintain access to water and a cool environment. Avoid prolonged physical exertion without breaks.
- Space sessions widely. Serotonin depletion requires weeks to recover from. A minimum of one month between uses is a conservative baseline; longer is better for both neurotoxicity risk and tolerance management.
- Inform a sober person of what you have taken, how much, and when.
Set & Setting
5-APB's effects are strongly shaped by environment. Entactogenic warmth dominates in social, comfortable settings; introspective or perceptual features become more prominent in quiet, solitary environments. The experience lasts 6–8 hours with residual effects extending beyond that — plan for a full day with no obligations.
A trusted, sober companion is valuable given the compound's capacity for disorientation and anxiety at higher doses. The physical environment should be temperature-controlled, as 5-APB impairs the body's thermoregulation.
Aftercare & integration. The serotonin depletion following 5-APB use produces a comedown that can last several days — low mood, irritability, difficulty concentrating, and disrupted sleep are common. This is neurochemical, not psychological: serotonin stores need time to rebuild.
During recovery, prioritize sleep, nutritious food, gentle physical activity, and social connection. Avoid making significant life decisions during the comedown period. If low mood persists beyond one week, or if unusual perceptual disturbances appear, consult a healthcare professional.
Recovery & Support
Compulsive use patterns with 5-APB are uncommon but not impossible — the dopaminergic component provides reinforcement, and psychological habituation to the entactogenic state can develop. If use has become a regular pattern despite negative consequences, or if increasing doses are needed for the same effects, professional support is warranted.
Substance use counseling, cognitive-behavioral therapy, and peer support groups experienced with stimulant or entactogen use are appropriate starting points. No 5-APB-specific treatment protocols exist; approaches used for MDMA-related concerns apply.
Recovery resources, crisis lines, and support pathways → View all
Emergency Response
Recognizing an emergency: body temperature you can feel through clothing. Seizures. Loss of consciousness. Chest pain or irregular heartbeat. Severe confusion or inability to communicate. Muscle rigidity with jerking movements (a sign of serotonin syndrome).
Immediate steps:
- 1. Call emergency services immediately if any of the above are present.
- 2. Move the person to a cool environment and remove excess clothing.
- 3. If unconscious but breathing, place in the recovery position (on their side, airway clear).
- 4. Do not induce vomiting. Do not restrain the person unless they are in immediate physical danger.
- 5. Monitor breathing continuously until help arrives.
What to tell the dispatcher: Name the substance (5-APB or benzofuran), the estimated amount, the time of ingestion, and current symptoms. Good Samaritan laws in many jurisdictions protect people who call for help during a drug emergency.
No specific reversal agent exists for 5-APB toxicity. Treatment is supportive — cooling, sedation, and monitoring.
Legal Status[edit]
International legal responses to 5-APB followed the pattern typical of novel psychoactive substances detected in the early 2010s: rapid national scheduling where NPS monitoring was established, and presumptive coverage under structural analog provisions elsewhere. 5-APB is not subject to any international scheduling instrument under the UN conventions, and legal status varies substantially by jurisdiction.
| Jurisdiction | Classification | Key provisions |
|---|---|---|
| United Kingdom | Class B (Misuse of Drugs Act 1971) | Temporary Class Drug Order from 10 June 2013;[9] permanent Class B from 10 June 2014.[8] Psychoactive Substances Act 2016 provides additional blanket coverage. |
| Germany | Anlage II BtMG (Schedule II) | Listed from 17 July 2013. Available by prescription only with strict controls.[4] |
| United States | Not explicitly scheduled | Likely covered by the Federal Analogue Act as a structural analogue of MDA (Schedule I). No specific DEA scheduling action confirmed.[4] citation needed |
| Australia | Likely covered under analog provisions | Structural similarity to MDA suggests coverage under analog scheduling. Not confirmed from primary government sources. citation needed |
| Canada | Likely covered under analog provisions | Similar compounds may fall under Schedule III. Not confirmed from primary government sources. citation needed |
references
- [1] ^abcBrandt SD, Walters HM, Partilla JS, Blough BE, Kavanagh PV, Baumann MH (2020) The psychoactive aminoalkylbenzofuran derivatives, 5-APB and 6-APB, mimic the effects of 3,4-methylenedioxyamphetamine (MDA) on monoamine transmission in male rats — Psychopharmacology doi:10.1007/s00213-020-05648-z
- [2]
- [3]
- [4]
- [5] ^abcKrpo M, Luytkis HC, Haneborg AM, Høiseth G (2018) A fatal blood concentration of 5-APB — Forensic Science International doi:10.1016/j.forsciint.2018.08.044
- [6]