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Phenibut

Group: Depressants
Nicknames: Anvifen, Fenibut, Bifren, Noofen, Phenigamma, Phenigama, Fenigam, F-but
Last reviewed: October 2026

Pharmacology

Phenibut has been classified as an atypical tranquiliser due to its mixed pharmacological action. Phenibut is a full agonist of the GABA-B receptor as well as a gabapentinoid, which block α2δ-1/2 calcium channel subunits (see Pregabalin for further information about gabapentinoids). Compared to baclofen and benzodiazepines, phenibut had considerably weaker anti-anxiety and tranquilising effects.

Alongside its GABA-mimicking and gabapentinoid effects, it has also been shown to stimulate dopamine receptors and block β-PEA in animal studies – a natural stimulating amine thought to contribute to anxiety.

There is not much research on the pharmacokinetics or toxicology of phenibut in animals or humans.

Interactions

The combination of phenibut with other depressants, such as opioids and benzodiazepines, is likely to carry the same increased risk of respiratory depression and overdose as other gabapentinoids. As opioid tolerance leads to more calcium channels in nerve cells, phenibut may also reduce opioid tolerance which can lead to accidental overdose. Drinking alcohol alongside taking phenibut can lead to increased sedative effects on the brain and body.

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