Nimetazepam (marketed under brand name Erimin®) is a hypnotic drug which is a benzodiazepine derivative. It possesses strong hypnotic, anxiolytic, anticonvulsant, sedative and skeletal muscle relaxant properties. It is sold in 5 mg tablets known as Erimin-5. It is used to treat insomnia.

Nimetazepam has a reputation for being particularly subject to abuse (known as ‘Happy 5’, sold as an Ecstasy replacement without a hangover), especially by persons addicted to amphetamines or opiates. For this reason it is no longer sold in most Western nations, but is still a significant drug of abuse in some Asian countries such as Japan and Malaysia. Nimetazepam is the only benzodiazepine to be subject to legal restrictions in Malaysia, and due to its scarcity, many tablets sold on the black market are in fact counterfeits containing other benzodiazepines such as diazepam or nitrazepam instead.^[1]

In a rat study Nimetazepam showed greater damage to the fetus, as did nitrazepam and especially temazepam when compared against other benzodiazepines. Diazepam however showed relatively weak fetal toxicities.^[2]