“Medical marijuana use may substitute prescription opioid use, whereas nonmedical marijuana use may be a risk factor of prescription opioid misuse. This study examined the associations between recreational marijuana legalization and prescription opioids received by Medicaid enrollees. In models comparing eight states and DC, legalization was not associated with Schedule II opioid outcomes; having recreational marijuana legalization effective in 2015 was associated with reductions in number of prescriptions, total doses, and spending of Schedule III opioids by 32%, and 31%, respectively. In models comparing eight states and DC to six states with medical marijuana legalization, recreational marijuana legalization was not associated with any opioid outcome. No evidence suggested that recreational marijuana legalization increased prescription opioids received by Medicaid enrollees. There was some evidence in some states for reduced Schedule III opioids following the legalization.” https://www.ncbi.nlm.nih.gov/pubmed/30390550

https://www.sciencedirect.com/science/article/pii/S0376871618307567?via%3Dihub