Supplement analysis backed by scientific evidence · PT

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Limited evidenceStress & mood

Phenibut

Phenibut is a prescription central nervous system depressant in several countries that is sold online in the US as a 'dietary supplement' — which it is not. It produces tolerance within days and a withdrawal syndrome resembling benzodiazepine or baclofen withdrawal, including seizures and psychosis.

What the science says

  • Reduces anxiety and social inhibition Limited evidence

    Phenibut is a GABA-B receptor agonist — essentially baclofen with a phenyl ring — developed in the 1960s Soviet Union and prescribed there at 250-500 mg for anxiety and insomnia. The supporting clinical literature is largely mid-20th-century Soviet work that predates modern trial standards; there are no contemporary, adequately powered, placebo-controlled trials in Western populations.

  • Safe for occasional use because it is 'just a GABA analogue' Limited evidence

    Reviews document that tolerance develops within days to weeks of regular use, driving rapid dose escalation from a few hundred milligrams to multiple grams daily. Withdrawal is a medical emergency: published cases describe agitation, insomnia, hallucinations, psychosis and seizures, typically requiring inpatient management with a baclofen or phenobarbital taper rather than simple cessation.

  • It is a legitimate dietary supplement Limited evidence

    Phenibut is a prescription pharmaceutical in Russia and Latvia (Anvifen, Noofen, Fenibut) and has never been approved in the US or EU. The FDA has stated that phenibut does not meet the statutory definition of a dietary ingredient and has issued warning letters to companies selling it; Australia scheduled it as a prohibited substance in 2018. US poison centres logged a steeply rising number of phenibut exposures over 2009-2019, with the great majority of cases occurring in the second half of that decade as online sales expanded.

Dosage & safety

Studied doseWe do not provide a recommended dose. For reference in interpreting case reports and prescribing information: prescription use abroad is 250-500 mg up to three times daily for short courses, while online users commonly report 1-3 g or more, and toxicity and dependence cluster at those higher self-administered doses. Onset is slow (2-4 hours), which drives redosing and accidental overdose. Anyone currently taking phenibut daily should not stop abruptly — taper under medical supervision.
SafetySedation, dizziness, nausea, hangover and next-day cognitive impairment are typical. Combined with alcohol, benzodiazepines or opioids it causes dangerous respiratory depression and is a recurring feature of intensive-care presentations. Overdose produces coma, agitated delirium and, occasionally, cardiotoxicity. Physical dependence can develop within two weeks of daily use, and withdrawal can be life-threatening — seizures, psychosis and delirium are documented. Phenibut is not approved as a supplement or drug in the US or EU, is prescription-only in Russia and Latvia, is a prohibited substance in Australia, and falls under psychoactive-substances legislation in the UK. It has caused positive results in workplace testing contexts and its use is inconsistent with the safety standards of any legitimate supplement. If you are using it and want to stop, contact a clinician or a poison centre for a supervised taper.

Scientific references

Where to buy

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