Phenibut
A GABA-B receptor agonist developed in the Soviet Union and used there as an anxiolytic. It produces calming and pro-social effects, but carries a well-documented risk of tolerance, dependence and a severe, sometimes protracted withdrawal syndrome — the most important fact about it.
01 Overview
Phenibut is a phenylated analogue of the neurotransmitter GABA, prescribed in Russia and several post-Soviet states for anxiety, insomnia and related conditions. Outside those markets it is unapproved and sold as an unregulated supplement, where it is frequently misused at high doses.
At low doses it reduces anxiety and can feel mildly euphoric and sociable. The central problem is its liability for tolerance and physical dependence: regular use leads to escalating doses, and abrupt cessation can produce a withdrawal syndrome featuring severe rebound anxiety, agitation, insomnia, autonomic instability and, in serious cases, psychosis or seizures. Withdrawal can be protracted, and medically supervised tapering is often required. Emergency departments and poison centres in several countries have reported rising phenibut dependence and withdrawal cases. This dependence/withdrawal profile is the dominant safety consideration and should not be understated.
02 Mechanism
Agonist at GABA-B receptors (with weaker GABA-A activity at higher doses) and antagonist at α2δ voltage-gated calcium channels, producing anxiolytic and sedative effects.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Low anxiolytic | 250–500 mg/day | Oral | Infrequent, non-daily use is strongly advised to avoid dependence; daily use readily produces tolerance. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Reduced anxietyCalming, anxiolytic effect used clinically in Russia. | Moderate | Observational | |
| Sociability / mild euphoriaUsers often report increased sociability and relaxation, contributing to misuse. | Variable | Anecdotal |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Sedation / next-day grogginessDrowsiness and hangover-like grogginess, potentiated dangerously by alcohol and other depressants. | Moderate | Common | Observational | |
| Dependence and withdrawal syndromeRegular use causes tolerance and physical dependence; abrupt cessation triggers severe rebound anxiety, agitation, insomnia, tremor, autonomic instability and, in serious cases, hallucinations, psychosis or seizures. Withdrawal can be protracted. | Severe | Common with regular use | Observational | |
| Overdose (sedation, agitation, loss of consciousness)High doses can cause profound sedation, paradoxical agitation, reduced consciousness and, in combination with other depressants, respiratory compromise. | Severe | With high doses | Observational |