Racemic phenibut (beta-phenyl-gamma-aminobutyric acid or 4-amino-3-phenylbutyric acid) is a neuropsychotropic drug that was discovered and introduced into clinical practice in Russia in the 1960s. In pharmacological tests of locomotor activity, antidepressant and pain effects, S-phenibut was inactive. In contrast, R-phenibut turned out to be two times more potent than racemic phenibut in most of the tests. Racemic phenibut and R-phenibut demonstrated an affinity for GABAB receptors, in contrast, S-phenibut was not able to bind receptors. Pharmacological activity of racemic phenibut relies on R-phenibut and this correlates to the binding affinity of enantiomers of phenibut to the GABAB receptor. Both S- and R-phenibut bind to the α2-δ subunit of voltage-dependent calcium channels and exert gabapentin-like anti-nociceptive effects. In addition S-isomer was found to be a substrate of gamma-aminobutyric acid aminotransferase, however, the R-isomer is a competitive inhibitor.