Medicaid expansion and opioid overdose mortality among socioeconomically disadvantaged populations in the US: A difference in differences analysis.

BACKGROUND

Opioid-related overdoses are a major cause of mortality in the US. Medicaid Expansion is posited to reduce opioid overdose-related mortality (OORM), and may have a particularly strong effect among people of lower socioeconomic status. This study assessed the association between state Medicaid Expansion and county-level OORM rates among individuals with low educational attainment.

METHODS

This quasi-experimental study used lagged multilevel difference-in-difference models to test the relationship of state Medicaid Expansion to county-level OORM rates among people with a high-school diploma or less. Longitudinal (2008-2018) OORM data on 2978 counties nested in 48 states and the District of Columbia (DC) were drawn from the National Center for Health Statistics. The state-level exposure was a time-varying binary-coded variable capturing pre- and post-Medicaid Expansion under the Affordable Care Act (an "on switch"-type variable). The main outcome was annual county-level OORM rates among low-education adults adjusted for potential underreporting of OORM.

FINDINGS

The adjusted county-level OORM rates per 100,000 among the study population rose on average from 10.26 (SD = 13.56) in 2008-14.51 (SD = 18.20) in 2018. In the 1-year lagged multivariable model that controlled for policy and sociodemographic covariates, the association between state Medicaid Expansion and county-level OORM rates was statistically insignificant.

CONCLUSIONS

We found no evidence that expanding Medicaid eligibility reduced OORM rates among adults with lower educational attainment. Future work should seek to corroborate our findings and also identify - and repair - breakdowns in mechanisms that should link Medicaid Expansion to reduced overdoses.