Effect of cannabis liberalization on suicide and mental illness following recreational access: a state-level longitudinal analysis in the USA

Objective To standardize the implementation dates of various cannabis liberalization policies and determine whether previous research by Anderson et al. [D.M. Anderson, D.I. Rees, J.J. Sabia, American Journal of Public Health 104, 2369-2376] on medical marijuana access and population-level suicidality is robust to additional years of data and further cannabis liberalization in the form of recreational marijuana access. Design A state-level longitudinal (panel) analysis. Suicide mortality rates from the National Center for Health Statistics and mental health morbidity rates from the National Survey on Drug Use and Health were employed with the procedures outlined by Anderson et al., using weighted ordinary least squares for three different specifications with various combinations of control variables as a sensitivity analysis to test for robustness. Setting All 50 states and Washington, DC for the period 1990-2020. Participants USA population. Interventions Cannabis liberalization policies in the form of recreational and medical access. Primary and Secondary Outcome Measures State-level population mental health outcomes in the form of suicide mortality among various age groups for males and females defined by the International Classification of Diseases, Ninth and Tenth Revisions; past-month and -year marijuana use, mental illness, serious mental illness, major depression, and suicidal ideation defined by the Substance Abuse and Mental Health Services Administration. Results Medical marijuana access was associated with a 3.3% reduction (95% CI -5.0% to -1.7%) in suicide rates for males, which was mediated by a 5.4% reduction (95% CI -8.0% to -2.7%) among males in the 30 to 39 age group. No other mental health outcomes were consistently affected by cannabis liberalization. Conclusions Adverse mental health outcomes do not follow cannabis liberalization at the state level, confirming the findings of Anderson et al. In addition, there is evidence that medical marijuana access reduces suicide rates for young-adult males. Strengths and limitations of this study Cannabis liberalization policies, which vary greatly throughout the literature, are explicitly defined and corrected from previous studies. SAMHSA suppresses state-level geographical information for individual-level responses in the NSDUH, so the analysis relied on population averages for a small number of age groups published in the NSDUH State Prevalence Estimates, which did not allow us to evaluate gender differences for mental health outcomes. The reliability of suicide and NSDUH data to estimate true population rates is highly debated. Population-level analyses of longitudinal data can be evaluated with multiple accepted methods from the medical literature and it is not clear whether weighted ordinary least squares is the most appropriate approach for this type of analysis. Funding statement This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Competing interests statement Reason Foundation is a 501(c)(3) nonprofit organization completely supported by voluntary contributions from individuals, foundations, corporations, and the sale of its publications. Reason Foundation’s general support includes contributions from marijuana manufacturers, which account for less than one percent of its annual budget. Data sharing statement Most data relevant to the study are publicly available and included as supplementary information. Mortality rates calculated from death counts of less than 10 deaths for any region are suppressed and may require special permissions for access.