Do Medical Marijuana Laws Reduce Opioid Use After Cancer Surgery?

Cross-sectional study using a difference-in-differences design with 2016–2022 private insurance claims data. N = 34,911 patients aged 18–64 undergoing resection surgery for breast (24,592), colorectal (8,510), or lung (1,809) cancer across 27 states without MML as of 2016. MML policies classified as: no MML, MML without dispensaries, and MML with dispensaries. Outcomes measured during 6 months post-diagnosis.

Cancer patients routinely receive opioids after surgery, and the opioid crisis has made clinicians and patients wary of these prescriptions. If medical cannabis can substitute for some strong opioid use after cancer surgery, that could reduce opioid-related risks—dependence, respiratory depression, constipation—without necessarily improving or worsening pain control. The dispensary access finding also matters for policy: laws on paper don't change behavior; actual access does.

This dovetails with RTHC-00158's finding that THC:CBD oil specifically improved pain in cancer patients but not overall symptoms. Together, they paint a picture of cannabis as a potential pain-specific tool in cancer care. The dispensary access finding also parallels broader health policy research showing that health laws only work when infrastructure supports them—a pattern seen in everything from ACA insurance mandates to naloxone access laws.

Private insurance claims only (excludes Medicare, Medicaid, uninsured). Ages 18–64, so doesn't capture older cancer patients who make up the majority. Claims data can't confirm whether patients actually used cannabis. The difference-in-differences design assumes parallel trends between legalizing and non-legalizing states, which may not hold perfectly. Cannot determine whether the opioid reduction improved or worsened pain outcomes.