Phenazepam belongs to the 1,4-benzodiazepines, the same family of medicines to which diazepam, oxazepam and temazepam belong. Phenazepam was first synthesized and developed in 1975 in the former Soviet Union where it became one of the most prescribed benzodiazepines since 1978 to treat sleep disorder, anxiety, alcohol use disorder and epilepsy. Phenazepam has not been licensed elsewhere in the world. The actions of phenazepam are mediated by the GABAA-receptor and reversed by the selective benzodiazepine antagonist flumazenil. In vitro, phenazepam and its metabolite 3-hydroxyphenazepam potentiate GABA responses with EC50-values of 6.1 nM and 10.3 nM, respectively, comparable to the value of 13.5 nM for diazepam. In vivo, phenazepam induces pronounced myorelaxation in the rotarod test with an ED50-value of 2.48 (1.65-3.72) mg/kg, and at 10 mg/kg it decreases punished responding in the conflict test (conflict between drinking motivation and painful electrical stimuli). Phenazepam increases the duration of sleep induced by hexanal several fold and is in this respect superior to diazepam. Both phenazepam and 3-hydroxyphenazepam are full GABAA receptor agonists.