VA-backed study finds veterans using medical cannabis reduced opioid prescriptions by 47%

A large-scale study backed by the Department of Veterans Affairs and published in JAMA Internal Medicine has found that veterans enrolled in state medical cannabis programs reduced their opioid prescriptions by an average of 47% within 12 months — with the reductions sustained over a three-year follow-up period.

The study

Researchers analyzed pharmacy records and medical data from 15,342 veterans across 12 states with legal medical cannabis programs. All participants had chronic pain diagnoses and active opioid prescriptions at baseline. The study compared opioid prescription patterns before and after medical cannabis enrollment, using a matched control group of veterans with similar pain profiles who did not enroll in cannabis programs.

Key findings

The results were striking:

• Veterans who enrolled in medical cannabis programs reduced their morphine milligram equivalents (MME) — the standard measure of opioid dosage — by an average of 47% at 12 months
• At 36 months, the average reduction was 52%, suggesting the effect was sustained and even strengthened over time
• 34% of participants discontinued opioids entirely within the first two years
• The matched control group showed only a 9% reduction in opioid use over the same period — consistent with broader national trends in opioid prescribing
• Participants reported statistically significant improvements in pain interference (how much pain affected daily activities), sleep quality, and overall quality of life

Dose-response relationship

The study found a dose-response pattern: veterans who used cannabis more consistently — as measured by dispensary purchase records — showed larger reductions in opioid use. This suggests the effect was driven by cannabis substitution rather than other confounding factors.

Veterans using cannabis at least 20 days per month showed a 58% reduction in opioid prescriptions, compared to 31% among those using cannabis fewer than 10 days per month.

Why this matters

The opioid crisis has killed more than 500,000 Americans since 1999. Veterans are disproportionately affected, with opioid prescription rates historically higher in VA healthcare than in the civilian population. Any intervention that meaningfully reduces opioid dependence among chronic pain patients has significant public health implications.

Previous studies have suggested a link between cannabis access and reduced opioid use, but most were ecological studies — looking at state-level trends rather than individual patient outcomes. This study's patient-level data and matched control design make it the most rigorous evidence to date.

The VA's evolving position

The study is notable for its VA backing. The VA has historically been constrained by federal cannabis prohibition — VA physicians cannot recommend medical cannabis, even in states where it's legal. However, the VA has increasingly supported cannabis research, and in 2024 issued updated guidance allowing VA healthcare providers to discuss cannabis use with patients without disciplinary consequences.

Limitations

The researchers acknowledged several limitations:

• The study is retrospective, not a randomized trial — the gold standard for establishing causation
• Self-selection bias is possible: veterans motivated enough to enroll in a cannabis program may differ in other ways from those who don't
• The study could not control for specific cannabis products or dosing used by participants
• Opioid reduction does not necessarily mean pain was equally well managed — though the self-reported outcomes suggest it was

The bottom line

The study adds to a growing body of evidence that medical cannabis access is associated with reduced opioid use. It doesn't prove that cannabis is a replacement for opioids in all cases, and the researchers emphasized that pain management should be individualized. But for the 15,000 veterans in this study, cannabis enrollment was associated with substantial, sustained reductions in opioid prescriptions — and improvements in the quality of life metrics that matter most to patients.