The effect of cannabis policies on treatment outcomes for cannabis use among U.S. adults.

BACKGROUND: Research has explored the impact of various medical cannabis policies on substance use treatment admission in recent years, but we know little about factors related to participants' treatment engagement and outcome. To fill this gap in the existing literature, this study used national data to examine the influence of cannabis policies (decriminalized, medical, and recreational) and referral sources (criminal justice vs. voluntary) on treatment completion and length of stay. METHODS: Data came from the Treatment Episode Data Set-Discharge (2006-2017) on adults 18+ whose primary drug at treatment admission was cannabis. Difference-in-difference analyses using logistic regression examined the effect of cannabis policies on outpatient treatment completion (yes/no; n = 2,192,807) and length of stay (more/fewer than 90 days; n = 1,863,585) in those with a criminal justice or voluntary referral source. RESULTS: Cannabis policy was not associated with treatment completion in either those with a criminal justice or voluntary referral source. Compared to individuals in states where cannabis use was strictly illegal, those in states with a decriminalization policy were less likely to stay in treatment for 91+ days regardless of the referral source. CONCLUSIONS: Cannabis policy appears to have a differential effect on treatment completion versus length of stay, with policy having no impact on successful treatment completion. Specifically, we found that decriminalization policies hinder treatment engagement past 90 days. In this sense, length of stay may be a more useful measure of treatment outcome for research than treatment completion moving forward. Furthermore, our study found that neither medical nor recreational policies affected length of stay or treatment completion, regardless of referral source.