BACKGROUND: While a key goal of liberalizing cannabis policy is to reduce harms related to criminal justice involvement, the degree to which this occurs and how it varies by policy format is uncertain. We completed a systematic review of changes in cannabis offences overall and across subgroups after cannabis policy liberalization. METHODS: A search of 7 databases was conducted for studies examining changes in cannabis offences, including arrests, charges, convictions, and referrals, before and after cannabis policy changes. Four types of cannabis policy change were considered: medical legalization, non-medical decriminalization, non-medical legalization, and non-medical commercialization. Changes for each policy change were examined overall and across race/ethnicity, youth (<
18) vs adult (18 or 21+), and sex. Evidence was analyzed by Synthesis without Meta-analysis. RESULTS: From 2,806 studies, 17 studies set in North America were included (15 USA, 2 Canada). In regions where non-medical cannabis was criminalized, 0 % of studies (0/4) showed a significant reduction in cannabis offences after medical legalization, 100 % of studies (7/7) showed significant reductions after decriminalization, and 75 % of studies (6/8) showed significant reductions after non-medical legalization with reductions in offences ranging from 13.5 % to 78.0 % for decriminalization and 33 % to 87 % for legalization. In jurisdictions that had decriminalized cannabis use, non-medical legalization was associated with further significant reductions in cannabis offences in 67 % of studies (2/3), with reductions in offences ranging from 35 % to 84.2 %. There were insufficient studies on the effects of expanded non-medical commercial access (n = 2). Decriminalization was associated with a significant reduction in cannabis offences in all studies in youth (5/5) and 85 % of studies in adults (6/7). However, legalization was associated with significant reductions in youth offences in 33 % (1/3) of studies compared to 100 % (4/4) of studies in adults. Despite absolute reductions in cannabis offences after decriminalization and legalization across racial and ethnic groups, changes in relative disparities between groups were variable, increasing in some cases while decreasing in others. CONCLUSION: Non-medical cannabis decriminalization and legalization are both associated with reductions in cannabis offences. Reductions in cannabis offences were consistently observed after legalization in adults but were not consistently observed in youth. Persistent socio-ethnic disparities in cannabis offences emphasize the need for additional mitigation strategies.