OBJECTIVES: To evaluate opioid and medication-assisted treatment (MAT) utilization in Medicaid managed care plans in six states and the District of Columbia. METHODS: A post-hoc analysis evaluated opioid and MAT claim utilization (per thousand members [PK]) and expenditures (per member per month) from AmeriHealth Caritas’ claim database over a 24-month period (October 2015 to September 2017). Pearson’s correlation analyses were performed between MAT and opioid use with one-month lag periods. All analyses were performed with SAS EG 7.1 software. RESULTS: AmeriHealth Caritas paid out 2,695,303 distinct opioid claims (N=561,682 members) over the study period; 26,019 members with ≥24 claims and 389 prescribers accounted for 32.4% and 20.0% of all opioid claims, respectively. Members with multiple claims in high-risk strata included ≤18 year-olds; expectant moms; “Triple-Threat” users (opioid+benzodiazepine+carisoprodol); and moderate users. Opioid utilization and expenditures declined by 28.2% and 28.9%, respectively, while individual member claims declined by 18.3% (4.49% to 3.67%). For opioid-based pain management, decreases were observed in hydrocodone-acetaminophen (−19.4%), oxycodone-acetaminophen (−38.0%), tramadol (−19.5%), oxycodone (−30.3%), and acetaminophen-codeine #3 (−31.3%). For MAT-administered opioid addiction treatment, brand buprenorphine-naloxone decreased (−70.7%), while increases were observed in generic buprenorphine-naloxone (+903.0%) and buprenorphine (+68.8%), and the opioid receptor antagonists injectable naltrexone (+208.3%) and naloxone (+197.5% in 2017). Despite a 9.1% increase in MAT claims PK, MAT expenditures declined by −20.5% PK, correlating with decreased brand-to-generic buprenorphine-naloxone utilization (r=0.82, p<0.001). An inverse cross-correlation was observed between MAT and opioid use (r=−0.74, p<0.001). Inter-MAT and inter-opioid analysis show high correlations between current and prior-month’s use (r=0.56 and 0.77, respectively). Pain-related service utilization and opioid-related emergency department visits PK both decreased slightly over the study period. CONCLUSIONS: Fewer member claims for opioid pain management medications caused declines in opioid utilization, inversely correlated with increased MAT utilization for treating opioid addiction. Decreased brand-versus-generic buprenorphine-naloxone utilization was also correlated with lower opioid expenditures.