Review of Canada's cannabis legalization finds mixed and inconclusive public health impacts after four years | Research

The takeaway

Four years after Canada legalized recreational cannabis, evidence shows increased use in some groups, a shift away from smoking, mixed data on hospitalizations, and increasing but incomplete migration to legal sources.

Policymakers, public health professionals, and researchers in jurisdictions considering or evaluating cannabis legalization.

Mixed and inconclusive picture across four key public health indicators

What the researchers found

Cannabis use increased in select population groups, with a shift away from smoking toward other consumption methods. Evidence on cannabis-related hospitalizations for mental health was mixed. Cannabis-impaired driving prevalence was generally steady but THC exposure among crash-involved drivers may have increased. More users obtained cannabis from legal sources, but regular users continued using illicit sources.

Why it matters

As the first G7 nation to legalize recreational cannabis, Canada serves as a natural experiment for the world. This review provides the most comprehensive early assessment of public health impacts.

The numbers in context

The review covers four key indicators (use prevalence, hospitalizations, impaired driving, and sourcing) across the 2018 legalization period. Specific numbers vary by indicator and data source.

How the study worked

Review of peer-reviewed and grey literature featuring population-level or quasi-representative samples with comparable pre- and post-legalization outcome data for key public health indicators in Canada.

What this study cannot tell us

Short post-legalization timeframe limits detection of longer-term trends. Data sources vary in quality and representativeness. COVID-19 pandemic overlapped with the post-legalization period, confounding analysis. Some indicators have significant measurement challenges.

How to read the evidence

Comprehensive review of available data, but limited by short post-legalization timeframe and pandemic confounding.

When this study was published

Published in 2022, assessing impacts through approximately 4 years post-legalization.

The bigger picture

The mixed results challenge both proponents and opponents of legalization. Fears of dramatic increases in harm have not clearly materialized, but neither have clear public health improvements, suggesting legalization's effects may be more nuanced than either side predicted.

Questions still open

Will trends become clearer with more years of data? How much has COVID-19 confounded post-legalization outcomes? Are there subpopulations experiencing disproportionate harms that aggregate data obscure?

Common questions

Has cannabis use increased since Canada legalized it?

Use has increased in some population groups, and there has been a notable shift away from smoking toward other consumption methods like edibles and vaporizers. However, the overall picture is complex and varies by demographic.

Are people buying legal cannabis or still using the black market?

Increasing proportions of users are purchasing from legal sources, but some users, especially regular consumers, continue to use illicit sources, suggesting the legal market has not fully displaced the illegal one.

Read the original research

Developments and Changes in Primary Public Health Outcome Indicators Associated with the Legalization of Non-Medical Cannabis Use and Supply in Canada (2018): A Comprehensive Overview.

International journal of mental health and addiction, 1-15

View on PubMed ↗Publisher’s paper ↗

Citation

Boury, Himani; Hall, Wayne; Fischer, Benedikt. (2022). Developments and Changes in Primary Public Health Outcome Indicators Associated with the Legalization of Non-Medical Cannabis Use and Supply in Canada (2018): A Comprehensive Overview.. International journal of mental health and addiction, 1-15. https://doi.org/10.1007/s11469-022-00986-9