The opioid epidemic disproportionately impacts the American Indian (AI) population, which experiences an 88% higher prevalence of OUDs (1.5%) than the US general population (0.8%). The AI population is second only to non-Latinx whites in their experience of opioid overdose deaths (13.9 and 17.5 per 100,000, respectively). Fortunately, medication-assisted treatment (MAT; e.g., buprenorphine + naloxone) is highly effective for reducing opioid-related harm, including overdose, making it the gold-standard OUD treatment approach. A systematic review showed a median retention of 56% at the NIDA-recommended 12-month treatment length. However, most AI people with OUD do not attend traditional substance-use treatment (62%). This is concerning because treatment retention is strongly associated with a mortality rate reduction. Although no studies have documented OUD treatment outcomes specific to AI patients, research in Native communities has generally highlighted concerns about the cultural acceptability of the highly directive, Western medical substance-use treatment approaches (e.g., cognitive-behavioral therapy, 12-step programming) that are widely available. Further, previous research has indicated that AI patients with substance use disorders want greater representation of Native staff and better integration of culturally adapted approaches in the services they receive. Culturally adapted approaches to treatment are associated with reductions in use and associated harm. However, there are currently no evidence-based, culturally adapted counseling approaches for AI patients addressing MAT retention and opioid-related harm. Accordingly, the investigators are conducting a 2-phase R61/R33 development and evaluation project. The 2-year R61 Phase has been completed and entailed two parts. First, the investigators conducted a mixed methods inquiry to inform research methods and to create a community-specific, cultural adaptation of an existing, efficacious, harm-reduction counseling approach. Second, the investigators co-created and manualized the resulting Counseling for Harm Reduction and Retention in MAT at Cherokee Nation (CHaRRM-CN) together with a community advisory board comprising CNHS providers, staff, and patients as well as researchers from Cherokee Nation, Washington State University, and the University of Washington. The current, 3-year R33 Phase entails a 2-arm RCT (N=136) conducted within CNHS testing the efficacy of CHaRRM-CN in improving 6-month MAT retention, reducing substance-related harm and illicit opioid use, and increasing Native enculturation compared to a treatment-as-usual control condition.