Impaired driving is a major cause of preventable death worldwide. Alcohol-impaired driving accounted for a mean of 19% (range, 3%-34%) of the motor vehicle crash deaths in 20 countries in 20161; in 2018, 29% of the 36 560 crash deaths in the US were attributed to impaired driving.2By comparison, driving under the influence of cannabis was estimated to account for 8700 road traffic deaths worldwide in 2013.3 Alcohol and cannabis are often consumed together, and their combined use is associated with greater crash risk than the use of either substance alone.3 Notably, cannabinoids are the most commonly detected other drugs (besides alcohol) in fatally injured drivers (up to 15% in urban areas), and the prevalence is increasing.4,5