Research chemicalResearch chemicalEntactogenAmphetamine

4-MTA

Also known as 4-methylthioamphetamine · Flatliner · MTA

Written by enwyReviewed 4 Aug 20262 sources0 comments

4-MTA (4-methylthioamphetamine) is a particularly dangerous amphetamine-type serotonin releaser that also inhibits monoamine oxidase. It causes massive, poorly controlled serotonin release and has been directly implicated in multiple deaths. It is not a safe MDMA substitute and is described here as a hazard, not a recreational option.

01 Overview

4-MTA (4-methylthioamphetamine, 'flatliner') is a ring-substituted amphetamine that both releases serotonin and acts as a reversible monoamine oxidase inhibitor. This combination floods synapses with serotonin while blocking its breakdown, an unusually dangerous mechanism.

A slow onset led users to redose, precipitating severe, sometimes fatal serotonin toxicity and hyperthermia. Several deaths in the late 1990s and early 2000s were attributed to 4-MTA, prompting international control. It is stated plainly here: 4-MTA is exceptionally hazardous, with a narrow margin between an active dose and life-threatening toxicity.

02 Mechanism

Potent serotonin-releasing agent combined with monoamine oxidase A inhibition, producing sustained, poorly controlled serotonin excess. The MAOI action makes serotonin syndrome and hyperthermia far more likely than with MDMA.

03 Dosing

Tier	Dose	Route	Notes
Threshold / hazard	20–40 mg	Oral	No safe dose is established; the toxic margin is narrow and deaths have occurred at recreational doses.
Reported (hazardous)	40–80 mg	Oral	Slow onset drove fatal redosing. This range is documented, not endorsed.

04 Effects

Effect	Magnitude	Evidence
Delayed, weak empathySlow-onset, muted MDMA-like effects that historically led users to dangerously redose.		Anecdotal
Mild stimulationModest stimulant effect disproportionate to the severe toxicity risk.		Anecdotal

05 Side effects

Effect	Severity	Frequency	Evidence
Fatal serotonin syndromeThe combined releaser/MAOI action has caused fatal serotonin toxicity - hyperthermia, seizures, DIC and multi-organ failure - documented in multiple deaths.	Life-threatening	A defining, common hazard of this compound	Observational
Severe hyperthermiaExtreme, refractory hyperthermia documented in fatal cases.	Life-threatening	Common in intoxications	Observational
Cardiovascular collapseSevere hypertension and cardiovascular instability contributing to death.	Life-threatening	Uncommon but reported in fatalities	Observational

06 Legal status

United Kingdom

Class A (Misuse of Drugs Act)

Controlled following deaths. · as of Jan 2026

United States

Schedule I

Controlled substance. · as of Jan 2026

07 References

4-MTA (4-methylthioamphetamine): risk assessment and fatalitiesEUDA/EMCDDA risk assessment

Deaths involving 4-MTAPubMed search

08 Discussion0 comments

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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.