Recent Advances in the Science of Cannabis-Impaired Driving

To examine cannabis-induced effects on driving performance. Prior systematic reviews consistently reveal that Δ⁹-tetrahydrocannabinol (THC) impairs driving performance. The present narrative review summarized evidence on the acute and residual effects of cannabis on driving performance from controlled experimental research completed in the past five years. Expanding on prior research, recent studies examine individual and combined effects of THC and cannabidiol (CBD), combined effects of cannabis and alcohol, and a variety of cannabis administration modes.

Cannabis with THC acutely impairs driving without significant residual deficits. CBD does not acutely impair driving performance, although relatively low doses (< 300 mg) were used in most studies. The combination of alcohol and THC results in additive effects that amplifies impairment. In line with prior research findings, cannabis-induced driving impairment is consistently observed within the first hour after use and impairment remains detectable for ~ 4-5 h post-inhalation; studies testing oral and sublingual cannabis administrations were sparse. Participants were willing and ready to drive shortly after using cannabis while their driving skills were objectively impaired.

Despite clear evidence of cannabis-induced driving impairment, a consistent impairment standard that can be used outside the laboratory is lacking. More research focused on sensitive biomarkers combined with technologically-advanced behavioral methods is needed to improve the precision and accuracy in determining cannabis-induced driving impairment. Future studies should focus on novel oral and oromucosal formulations emerging on the legal cannabis market.