Abstract: Is the opioid epidemic attributable to prescription painkillers becoming more accessible? I find that, for an average county, Medicaid expansions under the Affordable Care Act caused approximately 175,000 more opioid units to be prescribed per year, and 4 additional opioid-related deaths per year. Medicaid expansions explain nearly a third of the overall death toll. These results are driven largely by deaths of white men, and vary by local access to marijuana (a substitute painkiller). After estimating the interactive impact of Medicaid expansions and marijuana legalization on opioid-related deaths, I conclude that opioid mortality can be reduced without restricting opioid access.