Late-StageResearch compound

Phenibut

β-phenyl-GABA, GABA-B agonist, Russian prescription anxiolytic.

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WHAT IS PHENIBUT?

Detailed overview

Phenibut (β-phenyl-γ-aminobutyric acid) is a Soviet space-program development (1960s), an anxiolytic that, unlike GABA itself, crosses the blood-brain barrier. Mechanism: GABA-B receptor agonist (similar to Baclofen; PMC6494145), α2δ-1 voltage-gated Ca²⁺ channel modulation (similar to Pregabalin), striatal dopamine elevation (animal models), and **PEA antagonism** (phenethylamine reduction adds an anxiolytic arm). The **(R)-enantiomer** is the principal active isomer. Used as a medicine in Russia (Anvifen, Noofen); a **UK Class C controlled substance since 2024**; not approved elsewhere in Europe or the USA. ⚠️ **Strong tolerance after 2-3 days of daily dosing + severe physical dependence** – withdrawal resembles benzodiazepine withdrawal (delirium, seizures, rebound anxiety), a clinically treatment-requiring syndrome. Max 2× weekly occasional use recommended.

Mechanism

GABA-B agonist + Ca²⁺-α2δ

Half-life

~5 h

Legal status

Russia Rx / UK Class C (2024)

Safety

Side effects, stop signs, contraindications

Side effects · 7

  • Sedation, drowsiness and fatigue, especially at higher doses
  • Rapid tolerance buildup after just 2-3 days of continuous use
  • Physical dependence and benzodiazepine-like withdrawal syndrome (anxiety, insomnia, tremor, in severe cases seizures, delirium)
  • Rebound anxiety and irritability as the effect wears off
  • Nausea, stomach discomfort, loss of appetite
  • Hangover-like grogginess, impaired concentration and balance during the effect
  • At overdose, deep sedation, respiratory depression, loss of consciousness (especially combined with alcohol or other sedatives)

Contraindications · 6

  • Avoid during pregnancy and breastfeeding (risk of dependence and neonatal withdrawal)
  • Dangerous combined with alcohol, benzodiazepines, opioids and other CNS depressants (additive sedation, respiratory depression)
  • Contraindicated in those with a history of substance use disorder or addiction due to high dependence potential
  • Must not be stopped abruptly after prolonged use, as life-threatening withdrawal may occur; gradual tapering is required
  • Caution in renal impairment (excretion is predominantly renal, risk of accumulation)
  • Avoid driving and operating machinery during the effect due to sedation and slowed reaction time

Related Nootropics

Same therapeutic category

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MolekulaX Editorial Team·Source-verified · PubMed · FDA · EMA
Updated: June 19, 2026

The information here is strictly for educational and scientific purposes. It does not replace medical advice or clinical consultation, and it does not encourage illegal substance or pharmaceutical use. Data is sourced. When in doubt, consult your doctor.