Relationships of Changing State Cannabis Policies with Alcohol Policy Effectiveness and Alcohol or Cannabis Involvement in Motor Vehicle Fatalities.

Introduction: Alcohol use is an established and important risk factor for motor vehicle crashes (MVCs) and crash fatalities. The liberalization of cannabis policy across U.S. states could impact MVC fatalities involving alcohol or the co-use of alcohol and cannabis.

Methods: Mortality data were from the Fatality Analysis Reporting System in 50 states and Washington DC from 2010-2019. State-year Alcohol Policy Scores (APS) and Cannabis Policy Scores (CPS) were used as measures of policy exposure in multivariable mixed logistic regression models to estimate the adjusted odds ratio (AOR) of two blood alcohol concentration (BAC) thresholds and/or any detectable tetrahydrocannabinol involvement in crash fatalities.

Results: In fully adjusted models, a 10-percentage point increase in APS (representing more robust alcohol control policies) was associated with a 6.3% lower risk of a BAC> 0.00% (AOR: 0.937, 95% CI: 0.886-0.991) or involvement at a BAC ≥0.08% (AOR: 0.938, 95 CI: 0.888-0.992) among MVC decedents. However, there were no significant independent association between CPS and alcohol involvement. A 10-percentage point increase in CPS (representing more robust cannabis control policies) was associated with reduced odds of cannabis involvement (AOR: 0.956, 95% CI: 0.922, 0.991) or alcohol and cannabis co-involvement (AOR: 0.962, 95% CI: 0.928, 0.997).

Conclusions: More restrictive alcohol policies and cannabis policies were associated with reduced odds of MVC fatalities involving alcohol or cannabis, respectively. Cannabis policies did not affect protective associations between alcohol policies and alcohol involvement. However, more restrictive cannabis policies were protective for co-involvement of alcohol and cannabis.