Dr Rachel Lees Thorne is a Research Fellow in the Centre for Drug Use Research at the University of Bath. She completed her PhD in 2023, using epidemiological and clinical trial methods to investigate risk factors and treatment for cannabis use disorder. Her current research focuses on generation of evidence to inform public health and drug policy related to cannabis use harms.

Abstract

International cannabis policies and their association with cannabis use, cannabis use disorder, and other psychiatric disorders

Aims: We aimed to review the international evidence base on the association between cannabis policy changes and indicators of change in population-level cannabis use, cannabis use disorder and other psychiatric outcomes.

Methods: We searched PubMed, PsychNet, Global Health and Google Scholar for original research including studies from any jurisdiction globally that estimated associations between changes in a cannabis policy (occurring from 2000–25) and either cannabis use (including prevalence, frequency, potency, or quantity of cannabis) or any outcome related to psychiatric disorders (including prevalence and incidence of disorders, symptoms, or health-care admissions).

Results: Markers of increased commercialisation for non-medical cannabis in Canada and the USA were associated with increased prevalence of cannabis use and cannabis use disorder in adults, whereas evidence was inconsistent for incidence of psychotic disorders. Policies that limit commercialisation, such as strictly regulated legalisation of medical or non-medical supply, were less consistently associated with cannabis use or psychiatric disorders, but long-term evaluation is needed.

Conclusions: Policy approaches towards cannabis regulation could have distinct effects on public health harms. Evidence indicates that there is increased risk of cannabis-related harms after policy changes with markers of commercialisation.