Cannabis involvement among mass shooters increased after medical legalization began

Among mass shooters, cannabis involvement (use, possession, or distribution) was significantly higher from 1996 onward compared to before (11.2% vs 4.9%, p=0.002). No similar increase occurred among non-firearm mass murderers (4.8% vs 5.7%, p=0.76). Mass shooters with cannabis involvement were significantly younger (28.7 vs 33.5 years).

Analysis of publicly available media reports and court/police records for mass shooting events in the United States from 1900 to 2019. Cannabis involvement was compared before and after 1996 (California medical cannabis legalization). Non-firearm mass murderers served as a comparison group.

While this study cannot establish causation, it raises questions about whether increased cannabis availability may be relevant for a small subgroup of individuals vulnerable to violence, particularly given the known association between heavy cannabis use and psychosis in predisposed individuals.

This is a deeply controversial area. Cannabis use has increased dramatically since legalization, so higher rates among mass shooters could simply reflect population-level trends. The comparison with non-firearm mass murderers somewhat addresses this but cannot fully account for confounding factors.

Reliance on publicly available reports likely underestimates cannabis involvement across all time periods. Cannot establish causation. Cannabis involvement includes use, possession, and distribution, conflating different relationships with the substance. Population-level cannabis use also increased post-1996.