Effect of nonmedical cannabis legalization and exposure to retail stores on cannabis harms: a quasi-experimental study

Background — In 2018, Canada became the second country to legalize nonmedical cannabis and the first to allow a commercial retail market. Limiting the density of stores selling other legal substances is associated with reductions in use and harms; however, similar associations for cannabis are not well established.

Objective — To examine the association between exposure to cannabis retail stores and cannabis-related harms.

Design — Population-based natural experiment examining cannabis-attributable emergency department (ED) visits between 2017 and 2022.

Setting — Ontario, Canada.

Participants — 10 574 neighborhoods containing 6 140 595 persons aged 15 to 105 years.

Measurements — The opening of all cannabis stores in Ontario was tracked to identify neighborhoods that became exposed (cannabis store within 1000 m) over time. Absolute and relative changes in rates of cannabis-attributable ED visits were compared in neighborhoods after they became exposed with matched neighborhoods that remained unexposed.

Results — Cannabis-attributable ED visits were increasing over time before retail store openings. In neighborhoods that became exposed to a cannabis store, the rate of cannabis-attributable ED visits remained constant after stores opened. In contrast, in matched unexposed neighborhoods, the rate of ED visits decreased. Collectively, neighborhoods that were exposed to retail stores had a monthly increase of 1.30 cannabis-attributable ED visits per 100 000 persons (95% CI, 0.51 to 2.09; P < 0.001) compared with unexposed neighborhoods, which was equivalent to a 12% (CI, 6% to 19%) relative increase in the monthly rate of visits.

Limitation — Findings may be influenced by unmeasured confounding between exposed and unexposed neighborhoods.

Conclusion — Findings suggest that prohibiting stores in certain areas, limiting store density, or placing restrictions on the overall number of stores may offer public health benefits in countries pursuing legalization.