Impaired driving and legalization of recreational cannabis

Abstract

CMAJ | APRIL 6, 2021 | VOLUME 193 | ISSUE 14 E481 “D on’t drive high.” This is the message that the government of Canada wanted all drivers to take to heart after the legalization of recreational cannabis in October 2018. However, the association between the use of legal recreational cannabis and impaired driving is not clear. Although cannabis consumption has the potential to substantially impair psychomotor skills and cognitive functions — reducing performance on critical tracking and divided-attention tasks, slowing reaction time and increasing lane weaving1 — the influence of cannabis on driving tasks varies by individual, dose and methods of consumption, and time since consumption before driving.2 Some studies have found associations between cannabis use and impairment of driving — including in driving simulators, closed-course driving and epidemiologic studies3 — but others have not.4 Furthermore, the findings of studies are frequently confounded by users’ consumption of cannabis with other legal (e.g., tobacco, alcohol) and illegal (e.g., opioids, methamphetamines) substances,3 making it difficult to estimate the relative contribution of cannabis consumption to motor vehicle collisions. This in turn leads to difficulty in establishing the optimal approach to educating both health care providers and the public about the effects of cannabis, so as to deter driving under the influence of cannabis. We analyze the association between recreational cannabis legalization and fatal motor vehicle collision rates and discuss the implications of existing evidence for Canadian policy and physicians’ practice.