BACKGROUND: In 2023, British Columbia implemented a pilot illicit drug decriminalization policy aimed at addressing the high burden of illicit drug toxicity deaths, creating a need to examine its health system impacts. Although research on decriminalization has largely focused only on substance-related outcomes, broader mental health service utilization, including substance-related mental health care, among people who use drugs remains an insufficiently studied domain that this study seeks to address.

METHODS: In this single interrupted time series analysis of prevalent people who use drugs with prior care (PWUD-PC) in BC, we examined the proportion of people who accessed mental health and substance-related (MH-SR) services and their average monthly MH-SR visits one year before and after the decriminalization policy, stratified by physician visits, emergency department visits, and hospitalizations.

RESULTS: The population prevalence of PWUD-PC remained stable at 1.8% before and after decriminalization, and no statistically significant changes were observed in the proportion of PWUD-PC accessing MH-SR physician services and hospitalizations. The early period following decriminalization did not produce large shifts in overall MH-SR service use among PWUD-PC. Some movements in trends were seen in emergency department use, while several other outcomes, particularly in hospitalizations and physician visits, continued pre-existing trends.

CONCLUSION: Overall, we found stable patterns of MH-SR service engagement across the intervention period and small shifts in the post-intervention trends of average MH-SR service visits. These findings suggest that the early period following decriminalization did not lead to abrupt or large shifts in MH-SR service use among PWUD-PC.