4-FA
1-(4-fluorophenyl)propan-2-amine
Overview
4-FA belongs to Entactogens/Empathogens / Phenethylamines.
Effects
Subjective effects vary. What a substance feels like depends on dose, individual physiology,
mindset, and setting. The points below describe commonly reported effects, not guaranteed, uniform, or
desirable outcomes.
- A stimulant–entactogen hybrid: euphoria (some compare it to MDMA and amphetamine), increased energy and sociability, mood elevation, and feelings of warmth and empathy.
- The time-course is characteristic: more empathogenic/MDMA-like in the first few hours, shifting to a more purely stimulant, 'speedy' feel as it continues.
- Common unwanted effects include jaw-clenching (bruxism), appetite suppression, nausea, headache, a raised heart rate and insomnia.
- Duration is roughly 3–7 hours.
Dosing & duration
Harm-reduction note: These are commonly cited reference ranges, not a recommendation or a
“safe” dose. Potency, purity, body chemistry, tolerance, and drug combinations vary widely. Start
low, go slow, wait for full effects before redosing, and never assume an unknown product matches these
figures. Missing data is not evidence of safety.
Oral. Not a recommendation. 4-FA is taken orally. A controlled first-in-man study used single 100 mg and 150 mg doses. Given the documented risk of serious cardiac and cerebral events, often heralded by a sudden severe headache, higher doses and redosing are particularly dangerous, and any severe headache is a reason to stop and seek medical help.
Dose ranges
Light
≈50–75 mg
Common
≈100 mg (controlled-study dose)
Strong
≈125–150 mg (upper controlled-study dose)
Duration
onset
≈30–60 min
peak
≈1–2 h
total
≈3–7 h
Chemical & Physical Properties
| Formula | C9H12FN |
| Molar mass | 153.2 g/mol |
| State | Solid (usually the hydrochloride salt) |
| Melting point | Not reported |
| Boiling point | Not reported |
| Density | Not reported |
| Vapor pressure | Not reported |
| pKa | Not reported |
| LogP | 1.9 (predicted, XLogP3) |
| Solubility | Not reported |
| Refractive index | Not reported |
Identifiers & Synonyms
| CAS | 459-02-9 |
| CAS (enantiomer) | |
| PubChem CID | 9986 |
| InChIKey | DGXWNDGLEOIEGT-UHFFFAOYSA-N |
| InChI | InChI=1S/C9H12FN/c1-7(11)6-8-2-4-9(10)5-3-8/h2-5,7H,6,11H2,1H3 |
| SMILES | CC(CC1=CC=C(C=C1)F)N |
Synonyms
- 4-FA
- 4-FMP
- para-Fluoroamphetamine
- PFA
- PAL-303
- Flux
Pharmacodynamics & Biochemistry
4-Fluoroamphetamine (4-FA, 'Flux') is a ring-fluorinated amphetamine that acts as a substrate-type releasing agent and reuptake inhibitor at the noradrenaline, dopamine and serotonin transporters: a monoamine releaser with a profile sitting between amphetamine and MDMA. Release is most potent for noradrenaline (EC50 ≈37 nM), then dopamine (≈200 nM), then serotonin (≈730 nM). This mixed catecholamine/serotonin release gives it both classic stimulant effects and a milder entactogenic (MDMA-like) quality. It has only weak direct affinity for serotonin receptors (5-HT2A/2C Kᵢ in the micromolar range) and is a weak MAO-A inhibitor. A controlled first-in-man study found it produces a mild 'psychedelic' state intermediate between amphetamine and MDMA. Unlike its chloro- and bromo- analogues (4-CA, 4-BA), 4-FA does not cause long-lasting serotonergic depletion in animals: the C–F bond resists the metabolic activation thought to drive that neurotoxicity.
Biological targets
- NET
- DAT
- SERT
- 5-HT2A
Binding & functional measurements
| Target | Measurement | Species |
|---|---|---|
| NET | EC50 (release) 37 nM | Rat |
| DAT | EC50 (release) 200 nM | Rat |
| SERT | EC50 (release) 730 nM | Rat |
| 5-HT2C | Ki 7,800 nM | Human |
Pharmacokinetics
| Bioavailability | Oral (well absorbed) |
| Tmax | ≈1–2 h (onset 30–60 min) |
| Half-life | Approximately 8–9 h after controlled oral administration in humans, with observed estimates ranging from 5.5 to 16.8 h. |
| Vd | Not reported |
| Protein binding | Not reported |
| Metabolism | Hepatic. The 4-fluoro substituent resists CYP-mediated ring hydroxylation, slowing deactivation |
| Excretion | Renal |
Toxicology & Safety
Harm-reduction note: Toxicity and risk depend on dose, route, purity, combinations, setting, and individual
health factors. Missing harms should never be interpreted as evidence of safety.
Not reported
4-FA's most important hazard is cardiovascular and cerebrovascular: its use, especially at higher doses, has been linked to a cluster of serious cardiac events and cerebral haemorrhages (strokes) in the Netherlands, which led the Dutch authorities to ban it in 2017. A sudden severe headache during or after use is a recognised warning sign and a reason to seek urgent medical help. Like other stimulant releasers it raises heart rate and blood pressure and can cause hyperthermia (though less than PMA or 4-methylamphetamine), plus the usual amphetamine risks of insomnia, anxiety, appetite loss and a comedown. It should not be combined with MAOIs, other stimulants or serotonergic drugs. Limited data must never be read as evidence of safety.[2][7]
Legal Status
Legal note: Legal status can change over time and may vary by country, region, formulation, analogue status,
prescription context, and enforcement practice. Always confirm with current official sources before relying on this section.
US: Schedule I. UK: Class A. DE: BtMG Anlage I
Interactions & Contraindications
Drug interactions
MAOIs Risk of hypertensive crisis and serotonin toxicity, 4-FA is itself a weak MAO-A inhibitor.[2]
Stimulants (amphetamines, cocaine) Additive cardiovascular strain (heart rate, blood pressure, arrhythmia risk).[2]
SSRIs, SNRIs, Other serotonergic drugs Additive serotonergic load and serotonin-toxicity risk.[2]
Contraindications
Cardiovascular disease, hypertension or arrhythmia or a personal or family history of stroke or aneurysm (documented cardiac and cerebral-haemorrhage risk).[7]
Concurrent MAOI, SSRI/SNRI or other serotonergic medication concurrent MAOIs or serotonergic medication.[2]
Personal or family history of psychosis, schizophrenia or bipolar disorder
Pregnancy or breastfeeding
No interactions or contraindications listed.
Usage & Context
- A recreational research chemical that became notably popular in the Netherlands, where most users chose it for its particular effects rather than its (then) legal status, before the 2017 ban.
- Sometimes mis-sold or adulterated with related compounds (e.g. 2-fluoroamphetamine, 4-fluoromethamphetamine) and implicated in poisonings when combined with other drugs.
- Studied in controlled human research as a milder, shorter alternative to MDMA and amphetamine.
Sources & Evidence
- PubChem: 4-Fluoroamphetamine (CID 9986) — identifiers & computed properties
- Wikipedia: 4-Fluoroamphetamine — pharmacology, effects, toxicology & legal status CC BY-SA 4.0
- Nagai F, Nonaka R, Satoh Hisashi Kamimura K (2007). The effects of non-medically used psychoactive drugs on monoamine neurotransmission in rat brain. Eur J Pharmacol 559:132-7.
PMID 17223101 · doi:10.1016/j.ejphar.2006.11.075
- Rickli A, Hoener MC, Liechti ME (2015). Monoamine transporter and receptor interaction profiles of novel psychoactive substances: para-halogenated amphetamines and pyrovalerone cathinones. Eur Neuropsychopharmacol 25:365-76.
PMID 25624004 · doi:10.1016/j.euroneuro.2014.12.012
- Kuypers KPC, De Sousa Fernandes Perna EB, Theunissen EL, et al. (2019). A First-in-Man Study with 4-Fluoroamphetamine Demonstrates it Produces a Mild Psychedelic State. J Psychoactive Drugs 51:225-235.
PMID 30676284 · doi:10.1080/02791072.2019.1569286
- Toennes SW, Schneider D, Pogoda W, et al. (2019). Pharmacokinetic properties of 4-fluoroamphetamine in serum and oral fluid after oral ingestion. Drug Test Anal 11:1028-1034.
PMID 30912312 · doi:10.1002/dta.2595
- Linsen F, Koning RP, van Laar M, et al. (2015). 4-Fluoroamphetamine in the Netherlands: more than a one-night stand. Addiction 110:1138-43.
PMID 25808511 · doi:10.1111/add.12932
- DEA Diversion Control Division: Controlled Substance Schedules (4-FA placed in Schedule I, effective 2026-02-17)
- GOV.UK: Controlled drugs list (Misuse of Drugs legislation) — 4-FA is Class A OGL v3.0
- PubChem computed properties (CID 9986)