Counties in states that expanded Medicaid coverage under the Affordable Care Act (ACA) saw lower rates of opioid-related mortality than those in non-expansion states, according to a cross-sectional study.

Medicaid expansion was associated with a 6% lower rate of total opioid overdose deaths (RR 0.94, 95% credible interval [CrI] 0.91-0.98), Nicole Kravitz-Wirtz, PhD, MPH, of the University of California Davis School of Medicine in Sacramento, and colleagues reported in JAMA Network Open.

In particular, states that expanded Medicaid had an 11% lower rate of fatal heroin overdoses at the county level, and a 10% lower rate of deaths involving synthetic opioids other than methadone, they found.

"The Affordable Care Act was not designed to address the opioid overdose crisis directly," Kravitz-Wirtz told MedPage Today in an email. "But the legislation contains several provisions that led us, and other researchers, to suspect that it may be related to changes in opioid overdose-related harm."

Opioid-related deaths in the U.S. have skyrocketed over the past 2 decades, quadrupling from 3.3 to 14.9 per 100,000 deaths from 2001 to 2017. The CDC reported more than 70,000 drug overdose deaths in 2017, over two-thirds involving opioids.

The ACA granted states the ability to expand Medicaid to individuals up to 138% of the federal poverty level, which required provision of mental health and substance use disorder (SUD) services to those that received coverage. During the study period, 32 states and the District of Columbia adopted Medicaid expansion under the ACA.

To determine whether or not the expansion of Medicaid -- and access to substance use disorder services -- might affect the opioid overdose epidemic, the researchers used data from the National Vital Statistics System to count the number of annual opioid overdose deaths from 2001 to 2017 in more than 3,000 counties in 49 states (excluding Alaska) and the District of Columbia.

In their statistical analysis, the researchers introduced a 1-year lag to allow for policy changes to materialize. They also took into account any co-occurring policies that may have affected opioid-related harm, including prescription drug monitoring programs, overdose Good Samaritan laws, naloxone access laws, and medical marijuana legislation.

Kravitz-Wirtz and colleagues identified 383,091 opioid overdose deaths from 2001 to 2017. Overdoses involving natural and semisynthetic opioids accounted for 40.9% of all deaths -- the largest proportion of deaths across all counties and years. This was followed by deaths involving heroin (25.3%), synthetic opioids other than methadone (24%), and methadone (17.1%).

They found that Medicaid expansion was associated with an overall lower risk of opioid-related mortality, and the study estimated that expansion may have prevented approximately 1,600 to 8,000 opioid overdose deaths from 2015 to 2017.

"The observed association between Medicaid expansion and decreased total opioid overdose deaths and deaths involving heroin and synthetic opioids other than methadone is likely in part attributable to the ACA's inclusion of mental health and SUD services as essential health benefits," the researchers wrote. "Expanded Medicaid eligibility has substantially increased access to these services among the low-income population."

Rates of overdose fatalities involving methadone, however, increased 10% in expansion states, they reported. They said this finding deserves "further investigation" and underscores the importance of ongoing efforts to "address safety concerns associated with methadone for pain in tandem with Medicaid expansion."

There was also no association between Medicaid expansion and deaths involving natural and semi-synthetic opioids (RR 1.03, 95% CrI 0.98-1.08).

Study limitations included the use of ICD-10 coding of death certificate data, which may not reliably identify the specific substances involved in fatal overdoses; however, the researchers recognized this limitation by producing a secondary analysis that excluded states with high rates of underreporting, which yielded similar results. Other limitations were the inclusion of opioid deaths from the entire population, as opposed to exclusively Medicaid enrollees.

The investigators said that in the future, they hope to investigate specific Medicaid provisions that may be associated with opioid-related deaths, and expand the research to the association between expansion and opioid-related harms. However, this study still provides current, empirical evidence of how this policy has impacted the opioid epidemic, they said.

"At a broad level, we hope the findings of this study suggest to policymakers that providing expanded access to healthcare may be a key policy lever to address the opioid overdose crisis," Kravitz-Wirtz said.

Noa Krawczyk, PhD, of the NYU Grossman School of Medicine in New York City who wasn't involved in the study, told MedPage Today that understanding the association between access to Medicaid and opioid overdose deaths is valuable, especially in a landscape of changing healthcare policy.

Substance use disorders are often treated through multiple avenues of care, such as prescription drugs or therapy, Krawczyk added, explaining that people without insurance coverage may not be as likely to stay in treatment programs.

"There are so many pieces of the healthcare system that interact with opioid use disorder, and Medicaid provides further access to many of those services," Krawczyk said.