Marijuana Policy Bundles in the American States Over Time and Their Impact on the Use of Marijuana and Other Drugs

Systematic Review and Meta-Analysis: Medical and Recreational Cannabis Legalization and Cannabis Use Among Youth in the United States

OBJECTIVE

Dramatic changes in state-level cannabis laws (CL) over the past 25 years have shifted societal beliefs throughout the United States, with unknown implications for youth. In the present study, we conducted an updated systematic review and meta-analysis examining estimated effects of medical cannabis legalization (MCL) and recreational cannabis legalization (RCL) on past-month cannabis use among US youth.

METHOD

A systematic review was conducted following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, followed by a subsequent meta-analysis investigating the associations between state-level cannabis laws (ie, MCL vs non-MCL, and RCL vs non-RCL) and past-month cannabis use prevalence among US adolescents and young adults. Supplemental analyses examined age-group effects and design-related factors.

RESULTS

Our search identified 4,604 citations, 34 and 30 of which were included in qualitative and quantitative analyses, respectively. Meta-analysis of MCL studies identified no significant association between MCL and change in past-month youth cannabis use (odds ratio [OR] = 0.981, 95% CI = 0.960, 1.003). Meta-analysis of RCL studies showed significantly increased odds of past-month cannabis use (OR = 1.134, 95% CI = 1.116-1.153). Meta-analysis of more recent studies, however, showed a significantly increased odds of past-month cannabis use among both adolescents and young adults (OR = 1.089, 95% CI = 1.015,1.169, and OR = 1.221, 95% CI = 1.188,1.255, respectively).

CONCLUSION

Cannabis legalization has complex and heterogenous effects on youth use that may differ across law types. Our meta-analytic results showed modest positive effects of RCL on past-month cannabis use (more so in young adults than in adolescents) and minimal effects of MCL on these outcomes in US youth. Given the shift toward recreational legalization, additional focus on RCL effects is warranted.

Relationship between mandatory warning signs for cannabis use during pregnancy policies and birth outcomes in the Western United States

As U.S. states legalize recreational cannabis, some enact policies requiring Mandatory Warning Signs for cannabis during pregnancy (MWS-cannabis). While previous research has found MWS for alcohol during pregnancy (MWS-alcohol) associated with increases in adverse birth outcomes, research has not examined effects of MWS-cannabis. This study uses Vital Statistics birth certificate data from June 2015 - June 2017 in seven western states and policy data from NIAAA's Alcohol Policy Information System and takes advantage of the quasi-experiment created by Washington State's enactment of MWS-cannabis in June 2016, while nearby states did not. Outcomes are birthweight, low birthweight, gestation, and preterm birth. Analyses use a Difference-in-Difference approach and compare changes in outcomes in Washington to nearby states in the process of legalizing recreational cannabis (Alaska, California, Nevada) and, as a secondary analysis, nearby states continuing to criminalize recreational cannabis (Idaho, Montana, Wyoming). Birthweight was -7.03 g lower (95% CI -10.06, -4.00) and low birthweight 0.3% higher (95% CI 0.0, 0.6) when pregnant people were exposed to MWS-cannabis than when pregnant people were not exposed to MWS-cannabis, both statistically significant (p = 0.005 and p = 0.041). Patterns for gestation, -0.014 weeks earlier (95% CI -0.038, 0.010) and preterm birth 0.2% higher (95% CI -0.2, 0.7), were similar, although not statistically significant (p = 0.168 and 0.202). The direction of findings was similar in secondary analyses, although statistical significance varied. Similar to MWS-alcohol, enacting MWS-cannabis is associated with an increase in adverse birth outcomes. The idea that MWS-cannabis provide a public health benefit is not evidence-based.