Driving under the influence of cannabis (DUIC): A risky proposition?

When non-medical cannabis use was legalized in Canada in 2018, there was concern that prevalence of driving under the influence of cannabis (DUIC) would rise. Post-legalization survey data has revealed potentially interesting patterns. Prevalence of cannabis use rose among the adult population following legalization. Among cannabis users, prevalence of DUIC decreased. Yet across the full population (cannabis users and non-users), prevalence of DUIC did not increase in the years immediately following legalization, though more recent survey data (2022 and 2023) identified a slight rise in DUIC prevalence across the general population. In the first few years post-legalization, there was some mixed data suggesting a rise in motor vehicle collision (MVC)-related injuries and fatalities involving delta-9-tetrahydracannabinol (THC; the psychoactive compound in cannabis); however, some more recent data suggest that this rise in MVC-related injuries and fatalities involving THC has begun to return to pre-legalization levels. Why did prevalence of cannabis use increase, yet most data suggest that DUIC did not? Public health initiatives aimed at influencing risk perceptions of cannabis use may provide part of the answer. We explore here survey data examining cannabis users’ perceptions of health and safety risks of cannabis and DUIC. Our assessment supports continued use of health promotion materials and campaigns, but calls for more rigorous evaluation of the effectiveness of these health promotion campaigns. If the number of people who choose to use cannabis continues to rise, Canada may still see an increase in the number of DUIC cases despite the lower prevalence of DUIC among cannabis users.