Cannabis and driving - Questions and answers for policymaking
Consumption of cannabis afects cognitive and psychomotor performance in ways that can impair driving (Verstraete and Legrand, 2014; Hall et al., 2016). Cannabis contains a variety of cannabinoids, the most important being tetrahydrocannabinol (THC) and cannabidiol (CBD), which have very diferent efects on the brain. Te relative amounts of these and other cannabinoids in cannabis plants and cannabis products vary widely. Te THC in cannabis provides the predominant psychoactive efects and is considered to be mainly responsible for the impairment of function that afects driving ability.
Cannabis is a widely used substance. Within the general population, young adults have the highest rates of cannabis use (Canadian Centre on Substance Use and Addiction, 2017; EMCDDA, 2017) and are the age group at highest risk of motor vehicle crashes in the European Union (EMCDDA, 2012), Canada (Beirness and Porath, 2017), the United States (Substance Abuse and Mental Health Services Administration, 2017) and Oceania (Australian Institute of Health and Welfare, 2017).
The recreational use of cannabis has been legalised in nine states in the United States and in Uruguay (as of April 2018) and the Canadian government plans to legalise it in 2018. Tese developments have heightened concerns about cannabis and driving, for two broad reasons. First, they mean that, in these jurisdictions, cannabis use will no longer be illegal in itself, so laws on driving after consuming cannabis might become much more like those for alcohol. Second, if cannabis legalisation increases the number of individuals in the population who use the drug, then the number of people who drive after using cannabis may also increase. Te extent to which such an increase actually occurs is not clear (see question ‘Has cannabis legislation increased the number of cannabis-impaired drivers?’ on page 11). Evaluation of the impact of legalisation on both the extent of driving under the infuence of cannabis and the impact on road trafc accidents and associated injuries is therefore important.