Phenibut, sold under the brand names Anvifen, Fenibut, and Noofen among others,[1] is a central nervous system depressant with anxiolytic effects, and is used to treat anxiety, insomnia, and for a variety of other indications.

Phenibut was developed in the Soviet Union and was introduced for medical use in the 1960s.[5] Today, it is marketed for medical use in Russia, Ukraine, Belarus, Kazakhstan, and Latvia.[5] The medication is not approved for clinical use in the United States and most of Europe, but it is also sold on the Internet as a supplement and purported nootropic.[3][10] Phenibut has been used recreationally and can produce euphoria as well as addiction, dependence, and withdrawal.[3] It is a controlled substance in Australia, and it has been suggested that its legal status should be reconsidered in Europe as well.

Tolerance to phenibut easily develops with repeated use leading to dependency.[5] Withdrawal symptoms may occur upon discontinuation, and, in recreational users taking high doses, have been reported to include severe rebound anxiety, insomnia, anger, irritability, agitation, visual and auditory hallucinations, and acute psychosis.[3] Baclofen has successfully been used for treatment of phenibut dependence.

Baclofen, sold under the brand name Lioresal among others, is a medication used to treat muscle spasticity such as from a spinal cord injury or multiple sclerosis.[5][6] It may also be used for hiccups and muscle spasms near the end of life.[6] It is taken by mouth or by delivery into the spinal canal.

Discontinuation of baclofen can be associated with a withdrawal syndrome which resembles benzodiazepine withdrawal

Acute withdrawal symptoms can be eased or completely reversed by re-initiating therapy with baclofen.