Medical cannabis legalization associated with increased cannabis sales but not increased illicit drug use across 20 countries

Fixed effects panel regression across 20 countries (14 with legalized medical cannabis, 6 without) found a strong negative association between tobacco use and medical cannabis sales, while cannabis consumption showed a positive association with medical cannabis markets. Amphetamine use was negatively associated with MC sales, suggesting substitution dynamics. Legalization was associated with an average annual increase of 26.06 tons of MC sales, sustained over time. Excluding the US (a market size outlier), the effect was 20.05 tons.

Panel data from 20 countries analyzed using fixed effects regression and a dynamic Difference-in-Differences (DiD) approach with multiple time periods. Variables included tobacco use, alcohol consumption, amphetamine, cocaine, and cannabis prevalence, and GDP. Event study estimates assessed post-legalization trajectories.

One of the most persistent concerns about cannabis legalization is that it will increase use of other drugs. This multinational analysis finds the opposite for some substances, with tobacco and amphetamine use negatively associated with medical cannabis markets.

The gateway drug hypothesis predicts that cannabis legalization would increase use of harder substances. This cross-national evidence suggests the relationship may work in the opposite direction for some drugs, with medical cannabis potentially substituting for rather than leading to other substance use.

Ecological study design means population-level associations cannot be interpreted as individual-level causal effects. Country-level data may mask within-country variation. The US is a major outlier in market size, complicating cross-country comparisons. Differences in legalization frameworks, enforcement, and cultural contexts across countries limit comparability.