Both medical and recreational cannabis legalization were associated with small but significant increases in opioid use disorder prevalence among VHA patients, with the largest effects in older adults and those with chronic pain.
Policymakers evaluating cannabis legalization, veterans, and anyone following the cannabis-opioid substitution debate.
0.23 percentage point OUD increase in older veterans with chronic pain after recreational legalization
What the researchers found
OUD prevalence increased by 0.06 percentage points after medical cannabis law enactment and 0.07 points after recreational law enactment. The largest increase was among adults 65-75 after recreational legalization (0.12 points overall, 0.23 points among those with chronic pain). These findings did not support the hypothesis that cannabis legalization reduces opioid use disorder.
Why it matters
A common argument for cannabis legalization is that it could reduce opioid dependence by offering an alternative pain treatment. This large-scale study of veterans found the opposite association, though the absolute increases were small.
The numbers in context
Study covered 2005-2022, ~3.2-4.5 million patients/year. 86.7-95.0% male. OUD increased 0.06% after MCL, 0.07% after RCL. Age 65-75 after RCL: +0.12%. Chronic pain + age 65-75 after RCL: +0.23%. In states without cannabis laws, OUD decreased from 1.12% to 1.06%.
How the study worked
Staggered-adoption difference-in-differences analysis of VHA electronic health records from 2005 to 2022 (approximately 3.2 to 4.5 million patients per year). OUD was identified by ICD-9/ICD-10 diagnosis codes. Models adjusted for demographics, prescription opioid receipt, other substance use disorders, and time-varying state covariates.
What this study cannot tell us
VHA patients are predominantly male and older, limiting generalizability. OUD was measured by diagnosis codes, which depend on clinical detection and documentation. The study cannot determine whether cannabis use directly caused increased OUD or whether both increased due to shared underlying factors. The absolute increases are very small.
How to read the evidence
Large-scale difference-in-differences study using millions of VHA records over 18 years with robust statistical methods. Strong population-level evidence, though causal inference is limited by observational design.
When this study was published
Published in 2025 in JAMA Health Forum with data through 2022.
The bigger picture
This study contradicts the popular narrative that cannabis legalization reduces opioid harms. However, the absolute effect sizes are small, and the direction of causation is unclear. It is possible that cannabis legalization reflects broader substance use trends rather than causing increased opioid use disorder.
Questions still open
- Why might cannabis legalization be associated with higher rather than lower OUD? Is this an artifact of increased healthcare engagement or substance use screening in legalization states?
Common questions
Does this mean cannabis legalization is bad for the opioid crisis?
Why were older veterans most affected?
Read the original research
Cannabis Legalization and Opioid Use Disorder in Veterans Health Administration Patients.
JAMA health forum, 6(6), e251369
Citation
Mannes, Zachary L; Wall, Melanie M; Alschuler, Daniel M; Malte, Carol A; Olfson, Mark; Livne, Ofir; Fink, David S; Keyhani, Salomeh; Keyes, Katherine M; Martins, Silvia S; Cerdá, Magdalena; Sacco, Dana L; Gutkind, Sarah; Maynard, Charles C; Sherman, Scott; Saxon, Andrew J; Hasin, Deborah S. (2025). Cannabis Legalization and Opioid Use Disorder in Veterans Health Administration Patients.. JAMA health forum, 6(6), e251369. https://doi.org/10.1001/jamahealthforum.2025.1369