Recreational cannabis legalization in Canada did not lead to significant rise in usage among young adults, McMaster study shows

When recreational cannabis was legalized in Canada in 2018, concerns were raised that increased availability might lead to higher use in young adults – the age group that has the highest rates of cannabis use and related problems. To the contrary, however, a recent study conducted by McMaster researchers found that cannabis use and related problems decreased in a sample of high-risk young adults over the course of legalization.

The research, published in JAMA Network Open, followed 619 young adults in Ontario, from Feb. 2017 until Feb. 2020, a timeframe inclusive of pre- and post-legalization of recreational cannabis. The study tracked longitudinal data and followed high-risk young adults who reported regular substance use prior to legalization, including the majority reporting cannabis use. Researchers in this study pointed out that young adults generally decrease their recreational substance use as they get older –  a phenomenon called “aging out”.

The study found high-risk young adults showed significant overall decreases in both cannabis use and cannabis-related consequences, such as low energy or neglecting obligations. The biggest trends, though, were evident based on pre-legalization patterns. The most frequent pre-legalization cannabis consumers reported the largest decreases in both use and negative consequences. In contrast, young adults who reported not using cannabis pre-legalization showed a modest increase in use post-legalization, but no accompanying increases in negative cannabis-related consequences.

“Our study is a great example of why the ongoing monitoring of substance use behaviours is so essential for evidence-based decision making,” explains first author Amanda Doggett, postdoctoral fellow in the Peter Boris Centre for Addictions Research of McMaster University and St. Joseph’s Healthcare Hamilton. “We were able to measure cannabis use and experiences of cannabis-related consequences among the same people before and after legalization and observed trends that aligned with an expected aging out pattern.”

A limitation of the study is that it is not possible to determine whether the results would have been different in the absence of recreational cannabis legalization. The authors say the findings need to be compared to a control group, or a sample of similar young adults who aren’t from a region where legalization of recreational cannabis occurred. Doggett is collaborating with researchers from the United States to do exactly this type of comparison.

“What is particularly interesting about the group we studied is that many individuals were considered to be ‘high-risk’ in that they were already engaging in cannabis use pre-legalization,” remarks study supervisor James MacKillop, director of the Centre for Medicinal Cannabis Research and a professor in the Department of Psychiatry and Behavioural Neurosciences at McMaster University.

“If legalization was expected to have broad impacts on young adults, we should have seen that show up in this higher-risk group; we thought of this group as a ‘canary in the coal mine’ so to speak.”

The authors say the findings bridge a crucial knowledge gap and offer a foundation for future research. The findings help policymakers understand the broader impacts of cannabis legalization, and provide evidence to inform future public health policy. However, they emphasized reasons for exercising caution when interpreting the findings.

“These results reflect changes within the early stages of legalization, before the dramatic proliferation of storefronts, and are in individuals in the developmental window to be naturally growing out of cannabis use. They are by no means definitive about the impacts of legalization on young adult cannabis use,” said MacKillop.

Funding for this study was provided by CIHR and James MacKillop’s Peter Boris Chair in Addictions Research and Canada Research Chair in Translational Addiction Research.