Importance: Recreational cannabis legalization (RCL) has been advocated as a way to reduce the number of individuals interacting with the US criminal justice system; in theory, however, cannabis decriminalization can achieve this objective without generating the negative public health consequences associated with RCL. It is still unclear whether RCL can bring additional benefits in terms of reducing cannabis possession arrests in states that have already decriminalized cannabis.

Question: Is recreational cannabis legalization (RCL) associated with a reduction in cannabis possession arrest rates in US states that have already decriminalized cannabis; if so, does this change differ by age and race?

Findings: In this cross-sectional study using difference-in-differences analysis for data from 31 states, RCL was associated with a 40% reduction in cannabis possession arrest rates among adults in the 5 states that had already decriminalized cannabis between 2010 and 2019. This decrease was significantly smaller than that for the 4 states that had not decriminalized cannabis (76%), and there was no association between RCL and changes in youth arrest rates or disparities in arrest rates among Black and White individuals.

Meaning: These findings suggest that RCL was associated with decreased cannabis possession arrest rates among adults during the study period, even in US states that had already decriminalized cannabis.