What Happened After Canada Legalized Cannabis: A Five-Year Systematic Review
The implementation and public health impacts of cannabis legalization in Canada: a systematic review.
Bottom Line
Canadian cannabis legalization reduced arrests from 200+ to 50 per 100,000 and kept youth use stable, but increased adult ER visits by 22% and pediatric edible hospitalizations by 7.5-fold.
Why It Matters
As countries consider legalization, Canada serves as a real-world case study of what happens when cannabis becomes legal, showing both intended benefits and unintended health consequences.
The Backstory
On October 17, 2018, Canada became the second country in the world — after Uruguay — to legalize recreational cannabis nationally. Not a state-by-state patchwork like the United States. Not decriminalization. Full federal legalization, creating a regulated market for 38 million people overnight.
Every country watching cannabis reform was watching Canada. Proponents predicted the end of the black market, massive tax revenue, and stable public health outcomes. Opponents predicted a surge in youth use, a wave of impaired driving fatalities, and a mental health crisis. Five years later, Wayne Hall — one of the world's most cited cannabis epidemiologists — published a systematic review of what actually happened.
The answer was more complicated than either side expected.
The Researcher
Wayne Hall has been studying cannabis policy for longer than most countries have been debating legalization. An Emeritus Professor at the University of Queensland's National Centre for Youth Substance Use Research, Hall has served as the World Health Organization's expert adviser on cannabis since 1993 — the year he was invited to update a WHO report on cannabis health effects and never stopped.
He has published over 250 papers on substance use policy. In 2014, his comprehensive 20-year review of cannabis adverse effects became a standard reference — the paper that established driving under cannabis influence roughly doubles crash risk, and that regular adolescent use is associated with cognitive and psychiatric harm.
Hall occupies a rare position in the cannabis debate: respected by both public health officials and reform advocates for his even-handed approach. He doesn't campaign for or against legalization. He counts what happens afterward.
What Canada Was Trying to Do
The Cannabis Act (Bill C-45) had specific policy goals. Understanding what Hall's review found requires knowing what the benchmarks were.
What Actually Happened
The Numbers in Context
200 → 50
cannabis offences per 100,000 population, from 2010 to 2019. This single number represents the most unambiguous benefit of legalization — the end of mass cannabis criminalization in Canada. At the peak, cannabis arrests were consuming enormous police and court resources while disproportionately affecting marginalized communities.
For comparison, the United States still arrests approximately 350,000-500,000 people annually for cannabis offences, despite the growing patchwork of state legalization.
Hall et al. (2023)
7.5x
increase in pediatric hospitalizations for cannabis ingestion in four Canadian provinces after edibles became legal in October 2019. This is the most troubling unintended consequence. Edible cannabis products — gummies, chocolates, baked goods — are inherently attractive to children, and child-resistant packaging has proven insufficient.
The delay of edible legalization to October 2019 (one year after initial legalization) was supposed to give regulators time to prepare. The data suggests the safeguards were inadequate.
Hall et al. (2023)
The Black Market Question
One of the most important findings was that the black market is resilient but shrinking. Legal purchases rose from 23% to 68% of the market between 2018 and 2020, but that still meant roughly a third of cannabis purchases came from illegal sources.
The Edibles Problem
The staggered legalization — flower and oils in October 2018, edibles in October 2019 — created a natural experiment that made one thing clear: edibles are the highest-risk product category from a public health standpoint.
What People Get Wrong
Myth vs. Reality
The Evidence
Evidence-based analysis
Implications for the United States and Beyond
Canada's experience is the best available data for countries considering legalization, because it happened nationally and was tracked systematically. For Americans following legalization policy debates, the lessons are specific:
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Youth use won't explode. This was the single most common prediction of legalization opponents, and Canada's data clearly contradicts it. Age restrictions, marketing bans, and education appear to work.
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Edible regulation matters enormously. The pediatric ingestion data is the strongest argument for strict edible packaging, dosing limits, and product appearance regulations. Child-appealing products (gummies, chocolates) are a genuine hazard.
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The black market won't vanish without price competitiveness. Excessive taxation and regulatory burden keep illegal sources attractive. Jurisdictions that want to eliminate the black market need to compete on price.
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Emergency department capacity needs expansion. A 22% increase in cannabis-related ER visits is manageable for a well-resourced health system, but it's a real cost that legalization budgets need to account for.
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The criminal justice benefit is immediate and large. Of all the outcomes Hall tracked, the reduction in arrests is the most unambiguous. The human cost of cannabis criminalization — disproportionately borne by marginalized communities — ends the day legalization begins.
Key Takeaways
The implementation and public health impacts of cannabis legalization in Canada: a systematic review
Hall W, Stjepanovic D, Dawson D, Leung J () · Addiction
Frequently Asked Questions
Cite this study
Hall, Wayne; Stjepanović, Daniel; Dawson, Danielle; Leung, Janni. (2023). The implementation and public health impacts of cannabis legalization in Canada: a systematic review.. Addiction (Abingdon, England), 118(11), 2062-2072. https://doi.org/10.1111/add.16274