• Yuyan Shi, Di Liang, Yuhua Bao, Ruopeng An, Mark S Wallace, and Igor Grant.
• Department of Family Medicine and Public Health, University of California San Diego, 9500 Gilman Dr, La Jolla, CA, 92093, USA. Electronic address: yus001@ucsd.edu.
• Drug Alcohol Depend. 2019 Jan 1; 194: 13-19.

ObjectivesMedical 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.MethodsState-level quarterly prescription drug utilization records for Medicaid enrollees during 2010-2017 were obtained from Medicaid State Drug Utilization Data. The primary outcome, opioid prescriptions received, was measured in three population-adjusted variables: number of opioid prescriptions, total doses of opioid prescriptions in morphine milligram equivalents, and related Medicaid spending, per quarter per 100 enrollees. Two difference-in-difference models were used to test the associations: eight states and DC that legalized recreational marijuana during the study period were first compared among themselves, then compared to six states with medical marijuana legalized before the study period. Schedule II and III opioids were analyzed separately.ResultsIn 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% (95% CI: (-49%, -15%), p = 0.003), 30% ((-55%, -4.4%), p = 0.027), and 31% ((-59%, -3.6%), p = 0.031), 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.ConclusionsNo 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.Copyright © 2018 Elsevier B.V. All rights reserved.

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