Phenazolam was first synthesized in the 1980s as a potential pharmaceutical but was not approved for therapeutic use. Phenazolam currently is not explicitly scheduled or controlled in the United States. Phenazolam is structurally similar to bromazolam, the previous and current most commonly detected NPS benzodiazepine, differing by the addition of a chlorine atom on the benzene ring (hence its nickname “clobromazolam”). Phenazolam was first detected in 2016 in a seized drug product in Sweden. The first detection of this drug at the Center for Forensic Science Research and Education (CFSRE) was made in 2022 in a blood specimen tested in collaboration with NMS Labs. The positivity of phenazolam had steadily increased overall since 2024, with an observed upward trend in phenazolam positivity from Q1 to Q3 2025. In March 2024, the World Health Organization placed bromazolam under Schedule IV of the Convention on Psychotropic Substances of 1971. Similar to control actions for other NPS, the positivity of bromazolam is expected to decline as it is replaced among the illicit drug supply with other novel benzodiazepines like phenazolam.
In 2025, phenazolam has been identified in eleven blood specimens (antemortem and postmortem) and 33 drug materials that were tested at our laboratory. The blood specimens originated from across the United States, as well as the United Kingdom. The majority of postmortem cases were males with ages from 18 to 31 years. Phenazolam has been detected alone and alongside other drugs including other benzodiazepines, opioids, stimulants, and hallucinogens. NPS detected alongside phenazolam included nitazene analogues, orphine analogues, medetomidine, and bromazolam, among others.
