Early evidence of the impact of cannabis legalisation on cannabis use, dependence and the use of other substances: a cautionary tale from the US

Background

The past decade has seen unprecedented shifts in the cannabis policy environment, and the public health impacts of these policy changes will hinge critically on how they affect patterns of cannabis use, as well as the use and harms associated with other substances.

Objectives

This study aims to review existing research on how cannabis liberalization impacts cannabis use, use disorders, as well as use of other addictive substances, emphasizing evidence from studies using methods for causal inference and highlighting gaps in our understanding of policy impacts on evolving cannabis markets.

Methods

Narrative review focusing on quasi-experimental population-based studies for how medical cannabis laws and recreational cannabis laws affect cannabis use and use disorders, as well as use of or harms related to alcohol, opioids, and tobacco.

Results

Research suggests medical cannabis laws increase cannabis use among adults, and specific provisions of the laws (i.e., those associated with less regulated supply) may increase adult cannabis use disorders and commercialized markets may have spillovers to adolescent use. These same laws appear to reduce opioid-analgesic-related mortality, but the impacts of these laws on alcohol and tobacco use and harm remain uncertain. Research on of recreational cannabis laws is just emerging, but it will likely face similar methodological and data challenges to studies of medical cannabis laws.

Conclusion

Research on how medical cannabis laws influence cannabis use has advanced our understanding of the importance of heterogeneity in policies, populations, and market dynamics, but studies of how cannabis laws relate to other substance use often ignores these factors. Understanding the effects of recreational cannabis laws will require greater attention to the nuances of policies and patterns of consumption.