Cannabis Legalization Was Linked to Slightly Higher Opioid Use Disorder Rates Among Veterans
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- 0.23 percentage point OUD increase in older veterans with chronic pain after recreational legalization
- Evidence Grade:
- 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.
- Study Age:
- Published in 2025 in JAMA Health Forum with data through 2022.
- Original Title:
- Cannabis Legalization and Opioid Use Disorder in Veterans Health Administration Patients.
- Published In:
- JAMA health forum, 6(6), e251369 (2025)
- Authors:
- Mannes, Zachary L(10), Wall, Melanie M(16), Alschuler, Daniel M(4), 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
- Database ID:
- RTHC-07041
Evidence Hierarchy
Looks back at existing records to find patterns.
What do these levels mean? →Frequently Asked Questions
Does this mean cannabis legalization is bad for the opioid crisis?
The absolute increases in OUD were small (fractions of a percentage point), and the study cannot prove causation. However, it does not support the claim that legalization reduces opioid use disorder.
Why were older veterans most affected?
The study found the largest increases in OUD among veterans aged 65-75 with chronic pain after recreational legalization. This group may have complex pain management needs and higher baseline opioid exposure.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-07041APA
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
MLA
Mannes, Zachary L, et al. "Cannabis Legalization and Opioid Use Disorder in Veterans Health Administration Patients.." JAMA health forum, 2025. https://doi.org/10.1001/jamahealthforum.2025.1369
RethinkTHC
RethinkTHC Research Database. "Cannabis Legalization and Opioid Use Disorder in Veterans He..." RTHC-07041. Retrieved from https://rethinkthc.com/research/mannes-2025-cannabis-legalization-and-opioid
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.