Association between state cannabis laws and opioid outcomes: A systematic review.

Background: Through increasing cannabis availability, state cannabis legalization has been posited as one potential solution to the opioid crisis by providing an alternative to long-term opioid use for treating chronic pain. Forty U.S. states have legalized cannabis for medical use and 25 for recreational use. We systematically reviewed the literature to investigate the relationship of state medical and recreational cannabis legalization (MCL and RCL, respectively) to rates of opioid prescriptions, nonmedical use, opioid use disorder (OUD), opioid-related hospitalizations and emergency department visits, and overdose deaths. Methods: We searched EconLit, EMBASE, MEDLINE, and Web of Science Core Collection for English-language studies published through 10/21/25 that estimated MCL or RCL enactment effects on opioid outcomes compared to states that did not enact such laws. This study is registered with PROSPERO, CRD42023416119. Findings: Of 43 eligible studies, 18 investigated MCL, 11 investigated RCL, and 14 investigated both. Findings on MCL, RCL and opioid prescribing were mixed. No study found decreases in non-medical opioid use after MCL enactment; only one study found decreased non-medical use after RCL enactment. No studies found that MCL or RCL decreased OUD. MCL enactment was associated with lower opioid overdose mortality rates in earlier but not more recent studies; studies of RCL and opioid overdose fatalities had inconsistent results. Interpretations: The mixed study findings suggest that MCL and RCL are just two factors in a complex set of influences on opioid outcomes that require further study. Meanwhile, cannabis legalization should not be considered an effective policy for curbing the opioid epidemic.