Importance: In 2017, 47,600 Americans died of an opioid overdose. Medication assisted treatment is effective at treating opioid use disorder, but it is not available at most substance abuse treatment centers. Expanding insurance coverage may motivate treatment centers to add the capacity to provide MAT. Objective: To determine whether or not the ACA Medicaid expansion caused more treatment centers to add the ability to prescribe drugs for MAT. Design and Data: This quasi-experimental study uses a difference-in-differences design exploiting the variation in the date states expanded their Medicaid programs. The data is provided by the 2011-2017 National Survey of Substance Abuse Treatment Services (N-SSATS), conducted annually by SAMHSA. This survey includes roughly 14,000 treatment centers every year. Data were aggregated to the expansion group-year level. A difference-in-differences regression model was estimated for changed in the percent of centers offering MAT in expansion states vs non-expansion states. Outcome variable: Percent of centers offering MAT Results: The difference-in-differences analysis estimates a very slight difference in the percent of centers offering MAT before and after the expansion of Medicaid in 2014 between expansion and non-expansion states, producing a confidence interval of (-4.11%, 4.87%) centered at a mean of 0.38%. This estimate is insignificant. Conclusion and Implications: The Medicaid expansion had no significant effect on the percent of centers choosing to offer MAT. In order to increase access to MAT, policy makers will have to consider alternate incentives to motive treatment centers to add capacity.