Study looks at impact of cannabis use on road accidents

Apr 13, 2021

Since the legalization of recreational cannabis in October of 2018, a number of regulatory and public health measures have been implemented to prevent cannabis-impaired driving. Despite ongoing studies and data collection and analysis by Statistics Canada, the association between the use of legal recreational cannabis and incidence of impaired driving is still unclear.

A recent review research study published in the Canadian Medical Association Journal (CMAJ) has analyzed the association between the legalization of recreational cannabis use and fatal motor vehicle collision rates. Moreover, the authors also discussed several implications of existing evidence for Canadian policy and physicians’ practice.

According to the data analysis carried out by the researchers, legalization of recreational cannabis in United States jurisdictions may be associated with a small but significant increase in fatal motor vehicle collisions and fatalities. When extrapolated in the Canadian context, this data suggests that legalization of cannabis could result in up to 308 additional driving fatalities annually.

The researchers have recommended health care professionals educate patients about the safer use of cannabis products, including advising them against using cannabis and driving (particularly in combination with alcohol), with a recommended wait time of at least 6 hours between consuming cannabis and driving.

Currently, psychomotor assessments are performed at the roadside to test drivers for cannabis-related impairment, including the Standardized Field Sobriety Tests. However, the validity of these tests for detecting impairment due to cannabis is uncertain.

Biochemical measures of cannabis in blood, urine or saliva are also being used, in addition to psychomotor assessments, to determine the level of impairment. Specifically, Bill C-46 (2018) permits the police to perform roadside testing of saliva for THC, with several testing devices currently approved and others currently being evaluated. In addition, this bill also specifies threshold driving limits for THC (2–5 ng/mL and ≥ 5 ng/mL) with minimum impaired driving penalties and higher penalties for lower levels of THC if alcohol is also detected (≥ 2.5 ng/mL THC with blood alcohol concentration of 0.05). In addition, some provinces and territories may implement stricter policies related to cannabis-impaired driving (such as Quebec and Saskatchewan, which currently have zero-tolerance policies, with penalties for any detectable THC). However, legal experts have questioned the practical application of these limits and their ability to withstand legal challenges, since there has been no clear demonstration of correlation between THC levels and driving impairment.

The study authors conclude that the implementation of impaired driving regulations and educational campaigns, including federal THC driving limits and public awareness of these limits, can help to prevent potential increases in cannabis-impaired driving in Canada.

Currently, Canada’s Lower-Risk Cannabis Use Guidelines recommend specific evidence-based steps individuals could use to reduce their risk of several cannabis-related harms. These steps include choosing lower-potency cannabis products, limiting use, and choosing non-smoking methods of consumption such as vapourizers or edibles. However, the guidelines warn that despite edibles being safer for respiratory health, consuming them makes users more susceptible to ingesting larger doses and experiencing more severe impairment as a result of delayed psychoactive effects.