Phenibut

Phenibut is a synthetic central nervous system depressant developed in the Soviet Union in the 1960s, structurally a derivative of the neurotransmitter GABA with a phenyl ring added. It is prescribed as an anti-anxiety and sleep medication in a few countries such as Russia, Ukraine, Belarus and Latvia, under names including Anvifen, Fenibut and Noofen, but it has no approved medical use in the United States or most of Europe. In the US it is sold online and in some shops as a nootropic or calming supplement, though the FDA has ruled it does not qualify as a dietary ingredient. Its reputation as a mild smart drug understates its pharmacology, which is closer to that of a prescription sedative.

Phenibut acts primarily as an agonist at GABA-B receptors, the same broad inhibitory system targeted by baclofen, and at higher exposures also interacts with GABA-A receptors and voltage-gated calcium channels. Activating these inhibitory pathways slows central nervous system signaling, producing sedation, reduced anxiety and muscle relaxation. Because it crosses the blood-brain barrier readily, effects can be pronounced, and its GABA-B activity underlies both the calming effect and its capacity to produce tolerance and physical dependence with repeated use.

Reported effects include reduced anxiety, sociability, sedation and a sense of calm or mild euphoria. Onset is characteristically slow, often several hours, and duration is long, which is central to its risk profile: people may misjudge whether an amount has taken effect because it simply has not yet begun to act. Higher exposures produce heavy sedation, grogginess, dizziness, nausea and impaired coordination. As tolerance develops the calming effects diminish while the drug's hold on the user grows.

Phenibut's central danger is dependence and withdrawal resembling those of benzodiazepines and alcohol. Tolerance can develop within days to weeks, and abrupt cessation after regular use can trigger a severe withdrawal syndrome including rebound anxiety, insomnia, agitation, tremor, hallucinations and, in serious cases, psychosis or seizures; medically supervised tapering, sometimes using baclofen, has been described in the clinical literature. The slow onset drives a specific overdose pattern in which people take more before the first amount has taken effect, then become dangerously sedated hours later. As a CNS depressant, phenibut is especially hazardous combined with other depressants: alcohol, benzodiazepines, opioids or sedating medications can compound respiratory and central nervous system depression, which can be fatal. US poison-center calls involving phenibut rose sharply in the late 2010s, with cases of coma and death reported. Products are unregulated, so actual content and potency are unknown and may not match the label. If someone is unresponsive, breathing slowly, or cannot be woken, treat it as an emergency and call 911; Poison Control at 1-800-222-1222 can advise on exposures. This page has not yet been medically reviewed.