Cannabis Legalization and Opioid Overdoses in Canada: What a 2026 UQAM Thesis Found

Frédéric Pitz’s 2026 economics master’s thesis at Université du Québec à Montréal examined recreational cannabis legalization in the context of Canada’s opioid crisis. The goal was to test whether the 2018 policy change altered cannabis use, use of other drugs or the trajectory of accidental overdoses.

The thesis compared Canada with U.S. states that had never legalized recreational cannabis and used three quasi-experimental approaches: difference-in-differences, an event-study design and synthetic difference-in-differences. The analysis also considered variation by age and province.

The thesis reported a clear and robust increase in cannabis consumption after legalization. Available data on other drug use were not strong enough to identify a clear effect. For accidental overdoses, the analysis did not find a statistically significant change in Canada’s trajectory attributable to cannabis legalization.

A non-significant estimate means the study did not detect a clear effect on that outcome under its design and data. It does not prove that every pathway was unchanged. Policy can influence retail access, product sourcing, enforcement, social norms and substitution patterns at the same time, and those effects may move in different directions. The fentanyl era complicates overdose analysis The thesis notes that overdose mortality in Canada has been heavily shaped by fentanyl and the toxic unregulated drug supply. When one powerful factor dominates a population trend, detecting smaller policy effects becomes difficult. That is one reason a simple correlation between cannabis legalization and overdose counts would be misleading.

Quasi-experimental methods can strengthen causal inference compared with a basic before-and-after chart, but they still rely on assumptions about comparison groups, parallel trends, measurement quality and other policy changes. National results also do not establish what happened in every province, age group or individual.

This thesis is useful because it resists a common policy shortcut. It does not support saying cannabis legalization caused the opioid crisis, and it does not support saying legalization solved it. The evidence is better described as: cannabis use increased, other-drug evidence was inconclusive and no significant change in Canada’s overdose trajectory was detected.