Hydroxyzine in impaired driving investigations

Hydroxyzine (Vistaril©) is an unscheduled, first-generation antihistamine prescribed for nausea/vomiting, atopic dermatitis or eczema, and anxiety. It can produce adverse central nervous system (CNS) depressant effects such as fatigue, sedation, and impaired memory and concentration. Several clinical studies have shown hydroxyzine is able to impair driving and psychomotor function; however, no case series have been published highlighting driving performance and roadside observations in driving under the influence of drugs investigations (DUID). Between January 2017 and October 2024, 319 blood specimens submitted for DUID testing confirmed positive for hydroxyzine. Mean and median blood concentrations were 70 ± 79 and 48 ng/mL, respectively, with a range of 8.0-600 ng/mL. More than half of hydroxyzine positive drivers were female (57%) with a mean age of 42 years. Common drug combinations in this study involved antidepressants (74%), opioids (44%), and anticonvulsants (38%). Only seven cases have been reported involving a single substance, and four of these investigations have been presented. Behavioral observations included incoordination, slow and slurred speech, and difficulty following instructions on standardized field sobriety tests. Driving observations included erratic driving, crashes, driving in opposite lanes of travel, and running stop signs. This is concerning since hydroxyzine became the most identified antihistamine in this population in 2023 outpacing diphenhydramine.