Phenibut

non-nutrient/non-botanical

What is it

Phenibut (beta-phenyl-gamma-aminobutyric acid) is a synthetic GABA analog developed in the Soviet Union in the 1960s as a prescription medication for anxiety, insomnia, and other conditions. It is not approved as a medication in the United States or most Western countries, but it is sold in some places as a dietary supplement.

How it works

Phenibut is a chemical modification of gamma-aminobutyric acid (GABA), the brain's main inhibitory neurotransmitter, with an added phenyl group that allows it to cross the blood-brain barrier (GABA itself does not). In the brain, phenibut acts as an agonist at GABA-B receptors and, at higher doses, has activity at GABA-A receptors and inhibition of voltage-gated calcium channels. The net effect is anxiolytic (anxiety-reducing), sedative, and at lower doses mildly stimulating due to dopaminergic effects. Phenibut is rapidly absorbed orally, with onset of effects in 2-4 hours and a duration of action of 5-10 hours or longer. Regular use leads to physical dependence and tolerance; withdrawal can be severe.

Evidence for 3 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Anxiety / social anxiety (off-label, recreational use)

Grade C

Moderate evidence

Phenibut is approved as an anxiolytic in some Eastern European countries based on clinical studies. Quality of these studies by current Western standards is limited, but anxiolytic effects are well documented.

Sleep / insomnia

Grade C

Moderate evidence

Phenibut has sedative effects that have been used to treat insomnia in countries where it is licensed. Dependence risk and rebound insomnia after stopping make it a poor choice for sleep management.

Cognitive enhancement

Grade F

Limited evidence

Marketed in supplements as a 'nootropic,' but evidence for cognitive enhancement in healthy people is essentially absent. Sedative effects make significant cognitive enhancement unlikely.

2 commercial forms

Phenibut HCl (hydrochloride)

Faster onset, more acidic, larger doses needed by weight

The most common form sold in supplements. Onset typically 2-3 hours.

Phenibut FAA (free amino acid)

Less acidic, may have slightly different absorption

Less common form, sometimes preferred for taste and stomach tolerability.

Dosage

In countries where phenibut is a prescription medication, typical clinical doses are 250-500 mg up to three times daily for short courses. Supplement labels often list 250-500 mg per serving. Higher doses and chronic use substantially increase the risk of dependence and serious withdrawal.

When and how to take it

If used at all, take infrequently (no more than 1-2 times per week) to reduce dependence risk. Onset is slow (2-4 hours), so taking it for acute situations like before social events requires planning ahead. Avoid combining with alcohol or other depressants. Do not stack with sleep aids.

Safety

Phenibut has a high risk of dependence and severe withdrawal, including seizures, hallucinations, severe anxiety, insomnia, and tremor. Side effects include sedation, dizziness, nausea, and at higher doses respiratory depression and unconsciousness, especially when combined with alcohol or other CNS depressants. Phenibut intoxication has resulted in emergency department visits and hospitalizations.

Who should be cautious

Avoid use altogether outside of countries where phenibut is a prescribed and supervised medication. Particularly dangerous for people with substance use disorders, mental health conditions, respiratory disease, or those on CNS-active medications. Avoid in pregnancy and breastfeeding. Do not stop abruptly after regular use; medical supervision is needed for tapering.

Interactions

Phenibut interacts dangerously with alcohol, benzodiazepines, opioids, and other CNS depressants, increasing risk of respiratory depression and overdose. It may also interact with antiepileptic drugs, antidepressants, and antipsychotics. Concurrent use with stimulants does not mitigate the dependence risk.

Frequently asked questions

Is phenibut legal?⌄

Phenibut is not approved as a drug in the US, UK, or most EU countries. It is sold as a supplement in some jurisdictions but banned outright in others (Australia, Hungary, Italy, Lithuania). Regulations vary.

Is phenibut addictive?⌄

Yes. Regular use leads to physical dependence, tolerance, and severe withdrawal. Even moderate use over a few weeks can cause significant problems on stopping.

How dangerous is phenibut withdrawal?⌄

Withdrawal can include severe anxiety, insomnia, hallucinations, and seizures. Medical supervision is recommended for anyone with regular use trying to stop.

Can I combine phenibut with alcohol?⌄

No. The combination significantly increases the risk of respiratory depression, blackouts, and death. Many phenibut-related emergencies involve alcohol.

Should I take phenibut for anxiety?⌄

Safer alternatives exist. Even in countries where phenibut is licensed, it is recommended only for short-term, supervised use. Most experts advise against self-medicating with phenibut.

References

  • Phenibut (Wikidata) — Wikidata link
  • Phenibut (PubChem CID 14113) — PubChem link
  • Phenibut (ChEBI 136039) — ChEBI link

Track Phenibut with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

Coming to App Store

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.