The legalization of non-medical cannabis use in Canada occurred approximately three years ago. The Canadian population’s support of the policy has grown to a substantive majority (> 70%), but it is too early for a comprehensive assessment as to whether legalization in Canada has been a ‘successful’ policy experiment in achieving its public health and safety policy goals [2, 30]. Legalization requires time to be fully implemented and its effects to be assessed, but assessments to emerge are unlikely to be unequivocal or conclusive [5, 15, 31]. We provided an assessment of selected population-based cannabis use and supply indicators relevant to its public health and public safety outcomes from pre- to post-legalization. While the evolution of these indicators occurred over-time and is associated with legalization as a fundamental policy reform, the observations are mainly ecological in nature and possible changes do not allow for causal attribution to the intervention. Other, secular or independent factors may have driven or contributed to the developments observed.

On the basis of these data, we offer the following ‘big picture’ observations. First, the prevalence of cannabis use in the population may have slightly increased following legalization in Canada – a jurisdiction which already had a comparably high prevalence of use prior to legalization. The increases observed seem to have arisen primarily in mid- and older-age users but may also have occurred in those under the legal age of use, i.e., youth/teenagers whose access to cannabis was intended to be reduced by legalization. Such developments are confirmed by the international Tobacco Control Evaluation Project, where cannabis use (in the past 12 months) among respondents ages 16 to 19 years in Canada was found to have significantly increased between 2017 and 2019 (AOR 1.28, 95% CI 1.15–1.43; p<0.0001) [32]. Several of the increases in use also appear to extend pre-legalization trends. For example, in the CAMH Monitor, the increases observed in cannabis use for most age groups 2017 - 2019 extend pre-existing increase trends over multiple years prior to 2017. Moreover, the COVID-19 pandemic has been associated with increases in psychoactive substance use, including cannabis, that may have contributed to increases observed in 2020 data [33].

Second, there were no substantive signals of increases in daily- or near-daily use among current cannabis users, a primary predictor of increased risk of cannabis-related health harms (e.g., mental health and dependence) [34, 35]. However, these rates already have stood at comparably high levels on a population basis. Similarly, no discernable increases were noted in the population-prevalence of cannabis-impaired driving. Driving under the influence of cannabis is an important outcome indicator for public health because it increases the risk for motor-vehicle collisions and related injuries/deaths that represent a well-documented principal contributors to the cannabis-related burden of disease [36, 37]. This suggests that new deterrence-oriented legislation implemented with legalization and targeted prevention messaging in this area may have been effective [38, 39].

Third, there has been a steady diversification of modes of cannabis use and related cannabis products [40, 41]. While ‘smoking’ cannabis (e.g., ‘joints’) remains the predominant route of use among cannabis users in Canada, its overall share has been declining in favour of alternative use modes (e.g., vaping, edible use) and products (e.g., vape oils and edibles), all of which are legally supplied through the Canadian retail system established by legalization. Increases in these alternative use modes have also been reported by other Canadian study samples, including adolescent users [32]. These developments may lead to reductions in chronic health risks from cannabis smoking for users and others, while bringing possibly different challenges associated with alternative use modes (e.g., delayed effect onset and possible over-use/impairment from edibles, pulmonary health risks from vaping products) [42–44].

Fourth, there is evidence that Canadian cannabis users have been making a steady transition from ‘illegal’ to ‘legal’ sources of cannabis products. It is plausibly assumed that after 2020, the substantial majority of users will have been utilizing ‘legal’ sources to obtain their cannabis. As expected, it has been a gradual process for cannabis consumers to adjust to and embrace the availability of legal cannabis distribution after decades of forced reliance on the illegal cannabis market and supply [27, 45]. The percentage of users who access legal sources has also hinged on the gradual ramp-up and increasing availability of legal cannabis retail infrastructure and outlets, which has varied considerably across Canada [46, 47]. Increased legal cannabis access can be assumed to translate into ‘safer’ product use and related public health benefits based on the use of regulated, quality-controlled products [48]. On the other hand, the cannabis supply dynamics observed suggest that under-age cannabis users do not seem to experience increased difficulty with or reductions in access to cannabis products in the evolving reality contexts of legalization.