Canada's Recreational Cannabis Legalization and Medical Cannabis Patient Activity, 2017-2022.

Objectives. To estimate changes in medical cannabis patient activity after Canada's recreational cannabis legalization. Methods. I used linear regressions of interrupted times series models to analyze medical cannabis patient registrations per 10 000 residents, purchases per 100 registrations, and packages per purchase in Canada's 10 provinces between April 2017 and December 2022. I tested relationships between the recreational law's passage in June 2018, recreational sales starting in October 2018, and the arrival of edibles and vapes in December 2019. Results. Medical patient registrations initially increased; they slowed after the law passed and started decreasing after edibles became available. Medical purchasing frequencies initially decreased; they decreased further in proportion to recreational sales but stabilized after edibles became available. Medical purchase sizes were initially stable; they began increasing after edibles became available. Conclusions. Canada saw substantial decreases in medical cannabis patient registrations, but the remaining patients stabilized their purchasing frequencies and increased their purchase sizes. Public Health Implications. Other countries might see significant changes in patient usage of their medical cannabis systems after nationwide recreational cannabis legalization. (Am J Public Health. 2024;114(S8):S673-S680. https://doi.org/10.2105/AJPH.2024.307721).