Phenazepam is a potent 1,4-benzodiazepine that has gained notoriety among recreational drug users. First synthesized in Ukraine in the 1970s, it is one of the most commonly prescribed benzodiazepines in Russia and other commonwealth of independent state nations, where it is used therapeutically as a prescription drug. Reports of abuse are widespread and several European countries have taken steps to control its use. However, in the USA, phenazepam is not approved for use by the Food and Drug Administration, nor scheduled under the Federal Controlled Substances Act. Phenazepam is widely available on the Internet, and recreational drug users report a potency 10-fold greater than that of nordiazepam. We report a case of a 24-year-old male driver who was apprehended for impaired driving following a two-vehicle crash. The subject exhibited slurred speech and profound psychomotor impairment. Toxicology testing revealed phenazepam at a concentration of 76 ng/mL in blood, with no other drugs detected. This case report not only demonstrates the potential for adverse traffic safety consequences following the misuse of phenazepam, but also highlights the importance of analytical factors such as immunoassay cutoff concentration, cross-reactivity and comprehensive screening using chromatographic-based techniques for impaired driving investigations.