Early evidence of the impact of cannabis legalization on cannabis use, cannabis use disorder, and the use of other substances: Findings from state policy evaluations

Abstract

Background: The past decade has seen unprecedented shifts in the cannabis policy environment, and the public health impacts of these changes will hinge on how they affect patterns of cannabis use and the use and harms associated with other substances.Objectives: To review existing research on how state cannabis policy impacts substance use, emphasizing studies using methods for causal inference and highlighting gaps in our understanding of policy impacts on evolving cannabis markets.Methods: Narrative review of quasi-experimental studies for how medical cannabis laws (MCLs) and recreational cannabis laws (RCLs) affect cannabis use and use disorders, as well as the use of or harms from alcohol, opioids, and tobacco.Results: Research suggests MCLs increase adult but not adolescent cannabis use, and provisions of the laws associated with less regulated supply may increase adult cannabis use disorders. These laws may reduce some opioid-related harms, while their impacts on alcohol and tobacco use remain uncertain. Research on RCLs is just emerging, but findings suggest little impact on the prevalence of adolescent cannabis use, potential increases in college student use, and unknown effects on other substance use.Conclusions: Research on how MCLs influence cannabis use has advanced our understanding of the importance of heterogeneity in policies, populations, and market dynamics, but studies of how MCLs relate to other substance use often ignore these factors. Understanding effects of cannabis laws requires greater attention to differences in short- versus long-term effects of the laws, nuances of policies and patterns of consumption, and careful consideration of appropriate control groups.

Keywords: Cannabis; alcohol; drug policy; opioids; substitution; tobacco.

Figure 1.

Cannabis policy in the United States, laws in effect as of January 1, 2018. Decriminalization refers to policies that remove penalties associated with possession of small amounts of cannabis for personal use, with no protection for supply. Medical cannabis laws are laws that remove criminal penalties for medicinal cannabis use and some form of supply. CBD (cannabidiol)-only laws are medical cannabis laws that only permit certain low-delta9-tetrahydrocannabinol (THC) strains of cannabis to be used for medicinal purposes. Recreational legalization refers to laws that remove criminal and monetary penalties for the possession, use, and supply of cannabis for recreational purposes.

Figure 2.

Flow diagram of studies included in the review. ^aCounts do not sum to 42 as many articles considered multiple outcomes within the same study.