Veterans’ opioid prescribing fell modestly after cannabis laws, but causation…

BACKGROUND: Cannabis use for chronic pain is legal in many US states. Cannabis legalization may influence opioid prescribing among patients with chronic pain, although evidence remains mixed. OBJECTIVE: This study examined associations between medical and recreational cannabis law (MCL/RCL) enactment and opioid prescribing among Veterans' Health Administration (VHA) patients with chronic pain overall and by age. DESIGN: Using 2013-2022 VHA electronic health records, we extracted ICD-9/10-CM diagnoses of chronic pain and data on opioid prescriptions. We used staggered-adoption difference-in-difference models to estimate associations between MCL/RCL enactment and opioid prescribing. PARTICIPANTS: VHA patients aged 18 to 75 years with chronic pain diagnoses residing in the US. MAIN MEASURES: The primary exposure was cannabis legalization assessed with state-year variables to indicate MCL and/or RCL enactment. States were categorized yearly as No-MCL/RCL, MCL-only, and MCL/RCL. Primary outcomes were dichotomous variables (yes, no) indicating ≥ 30 days of prescription opioids, long-term opioid therapy (LTOT; ≥ 90 consecutive days of prescription opioids without a gap of > 15 days in supply), high-dose opioids (≥ 50 morphine milligram equivalents), and opioid and benzodiazepine co-prescriptions. KEY RESULTS: Compared to states without cannabis laws, MCL enactment was associated with reductions in ≥30-day opioid prescribing (-0.79 percentage points; 95% CI, -0.86 to -0.71) and LTOT (-0.34; 95% CI, -0.40 to -0.28), but smaller declines in high-dose opioid (0.09; 95% CI, 0.05 to 0.12) and opioid/benzodiazepine co-prescribing (0.11; 95% CI, 0.07 to 0.14). Following RCL enactment (vs MCL), reductions were observed in ≥30-day opioid prescribing (-0.14; 95% CI, -0.19 to -0.08), high-dose opioid prescribing (-0.33; 95% CI, -0.35 to -0.30), and opioid/benzodiazepine co-prescribing (-0.33; 95% CI, -0.36 to -0.31). Associations varied by age, with reductions generally more consistent among adults aged 65-75 years. CONCLUSIONS: Findings suggest that greater legal cannabis access may be associated with modest reductions in opioid prescriptions among patients with chronic pain, potentially reflecting changes in patient and clinician treatment decisions related to pain management.