Impacts of decriminalization and its subsequent amendment on drug possession incidents and charges in British Columbia, Canada: Interrupted time series analyses (2013–2024)

Background and aims Decriminalization of personal possession of select illegal drugs was implemented in British Columbia, Canada, for a three‐year period starting 31 January 2023; however, following perceived increases in public drug use and disorder, an amendment introduced on 7 May 2024 rolled back key provisions. We examined the impacts of decriminalization and the subsequent amendment on drug possession incidents and persons charged in drug possession incidents. Design Uncontrolled and controlled interrupted time series analyses were conducted using generalized additive models (January 2013 to December 2024). Setting Canada. Cases Drug possession incidents and persons charged in drug possession incidents in British Columbia and all other Canadian provinces combined. Interventions Decriminalization (February 2023 to April 2024) allowed adults to possess a combined total of 2.5 g of select illegal drugs. The amendment (May 2024 to December 2024) restricted possession to private residences, communal shelters and harm reduction or addiction treatment facilities. Interventions were coded as dummy measures, with the pre‐decriminalization period set as the reference period. Measurements Monthly crude rate of drug possession incidents per 100 000 and age‐standardized rate of persons charged in drug possession incidents per 100 000 based on the Uniform Crime Reporting Survey, which is an annual census of criminal incidents reported to federal, provincial and municipal police services in Canada. Results In the uncontrolled interrupted time series analyses, decriminalization was associated with a decrease [change in the log‐transformed rate (β) = −0.84, 95% confidence interval (CI) = −0.96 to −0.72], while the amendment was not associated with changes (β = −0.12, 95% CI = −0.32 to 0.08), in drug possession incidents in British Columbia. This pattern of findings was also observed in the controlled interrupted time series analyses after differencing all other provinces combined and British Columbia [change in the difference of the log‐transformed rates (β) = 0.85, 95% CI = 0.73–0.97 for decriminalization and β = 0.11, 95% CI = −0.09 to 0.31 for the amendment]. In the uncontrolled interrupted time series analyses, decriminalization was associated with a decrease (β = −0.63, 95% CI = −0.79 to −0.47), while the amendment was not associated with changes (β = −0.27, 95% CI = −0.55 to 0.001), in persons charged in drug possession incidents in British Columbia. This pattern of findings was also observed in the controlled interrupted time series analyses after differencing all other provinces combined and British Columbia (β = 0.61, 95% CI = 0.47–0.76 for decriminalization and β = 0.14, 95% CI = −0.08 to 0.36 for the amendment). Summary Decriminalization of personal possession of select illegal drugs was associated with decreases in drug possession incidents and persons charged in drug possession incidents in British Columbia relative to other provinces in Canada; the subsequent amendment reversed this progress.