ISSUES: Policy enforcement is crucial to achieve impacts on alcohol-related harm. It is not clear what level of enforcement intensity or dosage is necessary for addressing drink driving and related harms. Given competing enforcement demands and agencies resource constraints, understanding how much enforcement is sufficient to deter drink driving is critical. APPROACH: This systematic literature review followed Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA) guidelines to examine research about dosage effects of enforcement and related visibility on drink-driving outcomes, including motor vehicle crashes and fatalities. Risk of bias was assessed using the Cochrane Collaboration Effective Practice and Organization of Care tool and the JBI checklist. KEY FINDINGS: The 21 studies that met the inclusion criteria for this review differed in measures of enforcement dosage and outcomes, making it difficult to synthesise results across studies and draw conclusions about a threshold or optimal level of enforcement. Although most included studies found that sustained enforcement was associated with reductions in drink driving or related harms, only two studies tested an optimal dosage. Due to study design limitations, a substantial percentage of these studies must be considered with caution. IMPLICATIONS: Additional research with rigorous study designs with appropriate controls is needed to determine an optimal high visibility enforcement dosage level to help law enforcement agencies make realistic decisions about allocating enforcement resources to address drink driving. CONCLUSION: Consistent evidence about a drink-driving enforcement dosage threshold is lacking, partly due to an insufficient number of well-designed studies. Addressing challenges of conducting rigorous studies in community settings is crucial.

OBJECTIVE: This study examined whether recreational marijuana legalization (RML) and local retail availability were associated with marijuana and alcohol use and co-use among adolescents. METHOD: We investigated associations between RML and past-30-day marijuana and alcohol use and co-use, and moderating effects of retail availability of marijuana and alcohol, using data from the 2010-2011 to 2018-2019 California Healthy Kids Surveys (CHKS) of 9th and 11th grade students in 38 California cities. Multilevel mixed-effects logistic regression analyses were conducted, controlling for secular trends and student and city demographics. Additional analyses examined associations of RML and retail availability with co-use among subgroups of drinkers and marijuana users. RESULTS: For the full sample, RML was inversely associated with alcohol use but was not significantly associated with marijuana use or co-use with alcohol. However, significant interactions between RML and marijuana outlet density showed that there were increases in marijuana and alcohol co-use and alcohol following legalization in cities with higher densities of marijuana outlets. RML was positively associated with co-use among non-heavy and heavy drinkers, but inversely related to co-use among occasional and frequent marijuana users. A significant positive interaction between RML and marijuana outlet density indicated that RML was associated with increases in co-use for occasional marijuana users in cities with higher densities of marijuana outlets. CONCLUSIONS: RML was associated with increases in marijuana and alcohol co-use and alcohol use among California high school students, particularly those in cities with higher densities of retail cannabis stores, although this varied across alcohol and marijuana use subgroups.