The finding: states that legalized medical or recreational marijuana saw significant reductions in non-fatal opioid overdoses. Access to medical cannabis dispensaries was associated with a 15.47 percent reduction in non-fatal opioid overdoses per 100,000 enrollees per quarter. Recreational legalization tracked to an 11.92 percent reduction. Among adults aged 18 to 34, the medical dispensary effect was even sharper — a 23.27 percent reduction.