“Medical marijuana legalization was found to be associated with a lower odds of any opioid use. In states where marijuana is available through medical channels, a modestly lower rate of opioid and high-risk opioid prescribing was observed. Policy makers could consider medical marijuana legalization as a tool that may modestly reduce chronic and high-risk opioid use.” https://www.ncbi.nlm.nih.gov/pubmed/30684198

https://link.springer.com/article/10.1007%2Fs11606-018-4782-2