Association Between US State Medical Cannabis Laws and Opioid Prescribing in the Medicare Part D Population.

<h4>Importance</h4>Opioid-related mortality increased by 15.6% from 2014 to 2015 and increased almost 320% between 2000 and 2015. Recent research finds that the use of all pain medications (opioid and nonopioid collectively) decreases in Medicare Part D and Medicaid populations when states approve medical cannabis laws (MCLs). The association between MCLs and opioid prescriptions is not well understood.<h4>Objective</h4>To examine the association between prescribing patterns for opioids in Medicare Part D and the implementation of state MCLs.<h4>Design, setting, and participants</h4>Longitudinal analysis of the daily doses of opioids filled in Medicare Part D for all opioids as a group and for categories of opioids by state and state-level MCLs from 2010 through 2015. Separate models were estimated first for whether the state had implemented any MCL and second for whether a state had implemented either a dispensary-based or a home cultivation only-based MCL.<h4>Main outcomes and measures</h4>The primary outcome measure was the total number of daily opioid doses prescribed (in millions) in each US state for all opioids. The secondary analysis examined the association between MCLs separately by opioid class.<h4>Results</h4>From 2010 to 2015 there were 23.08 million daily doses of any opioid dispensed per year in the average state under Medicare Part D. Multiple regression analysis results found that patients filled fewer daily doses of any opioid in states with an MCL. The associations between MCLs and any opioid prescribing were statistically significant when we took the type of MCL into account: states with active dispensaries saw 3.742 million fewer daily doses filled (95% CI, -6.289 to -1.194); states with home cultivation only MCLs saw 1.792 million fewer filled daily doses (95% CI, -3.532 to -0.052). Results varied by type of opioid, with statistically significant estimated negative associations observed for hydrocodone and morphine. Hydrocodone use decreased by 2.320 million daily doses (or 17.4%) filled with dispensary-based MCLs (95% CI, -3.782 to -0.859; P = .002) and decreased by 1.256 million daily doses (or 9.4%) filled with home-cultivation-only-based MCLs (95% CI, -2.319 to -0.193; P = .02). Morphine use decreased by 0.361 million daily doses (or 20.7%) filled with dispensary-based MCLs (95% CI, -0.718 to -0.005; P = .047).<h4>Conclusions and relevance</h4>Medical cannabis laws are associated with significant reductions in opioid prescribing in the Medicare Part D population. This finding was particularly strong in states that permit dispensaries, and for reductions in hydrocodone and morphine prescriptions.