Prescription opioid availability and opioid overdose-related mortality rates in Medicaid expansion and non-expansion states

Abstract

Aims: To determine whether, in the United States, higher opioid overdose-related mortality rates (OOMR) in Affordable Care Act (ACA) Medicaid expansion states relative to mortality rates in non-expansion states have been mediated by increased prescription opioid availability.

Design: Separate mixed-effect regression models examined difference-in-difference effects of time and expansion status on Medicaid-reimbursed opioids measured in morphine milligram (mg) equivalents on all OOMR and on prescription OOMR. We used generalized structural equation models to test whether increases in Medicaid-reimbursed prescription opioid availability mediated OOMR post-Medicaid expansion.

Setting and participants: This study used national, serial, cross-sectional data for Medicaid-reimbursed prescription opioids, Medicaid enrollment information and annual OOMR for any opioids and for prescription opioids from 49 states and the DC pre- (2008-13) and post-ACA Medicaid expansion (2014-16).

Measurements: The outcome measures were OOOMR and Medicaid-reimbursed prescription opioid availability. The main input variables were time and ACA Medicaid expansion status.

Findings: Medicaid expansion states had larger increases in prescription opioid availability (b = 480, 357.8, P = 0.001) compared with non-expansion states. However, the largest increases in prescription opioid availability in expansion states were between 2009 and 2011, well before the ACA Medicaid expansion. Whereas expansion states also had higher any OOMR compared with non-expansion states (b = 3.6, P = 0.011), significant differences in prescription OOMR between expansion and non-expansion states did not emerge until 2015 (b = 1.4, P = 0.014) and 2016 (b = 4.0, P = 0.004), and Medicaid-reimbursed prescription opioid availability was not a significant mediator.

Conclusions: Increases in Medicaid-reimbursed prescription opioid availability in Affordable Care Act Medicaid expansion states in the United States do not appear to have mediated post-Affordable Care Act Medicaid expansion mortality rate differences, but there is still a possibility of lagged effects.

Keywords: Affordable Care Act; mediated-moderation models; medicaid expansion; opioid epidemic; opioid overdose-related mortality rates; prescription opioids.