The U.S. Department of Health and Human Services has declared the misuse of opioid prescription drugs as a public health emergency. The Affordable Care Act’s Medicaid expansion expanded the number of people with insurance and increased the demand for services related to substance abuse treatment. In the first part of this study, the researcher examines whether the Medicaid expansion reduced the likelihood of treatment delay. The second part of this study explores whether the length of stay for opioid use disorder treatment is significantly different in states that adopted Medicaid expansion versus states that did not. In both studies, the researcher analyzes administrative data from the Substance Abuse and Mental Health Services Administration to discover any treatment delays associated with the opioid treatments for the states that adopted the expansion versus the states that did not, and to determine whether there was a difference in the length of stay in the states that adopted the Medicaid versus the states that did not. A difference-in-difference approach is used in both studies to compare the states which adopted an optional Medicaid expansion to those non-adoption states. The evidence suggests that demand for opioid treatment services increased in expansion states as there is a decreased probability of obtaining treatment on the first day for initial requests for outpatient treatment. In addition, evidence suggests that Medicaid expansion increased the likelihood of staying longer in outpatient facilities, but not inpatient facilities. / Business Administration/Risk Management and Insurance