Marijuana Legalization and Mental Health

This study examines the effects of marijuana legalization on mental health. We use a difference-in-differences approach that leverages the staggered implementation of both medical and recreational marijuana legislation across U.S. states. We find that marijuana laws have a positive effect on marijuana use but have no effect on mental health overall. Nonetheless, null aggregate effects mask sharp heterogeneities across the age distribution. We show that elderly individuals, especially those with pre-existing health conditions, benefit from medical marijuana legalization in terms of better mental health, whereas legalizing recreational marijuana produces the opposite effect for younger individuals, especially if relatively healthy.