Hybrid Effectiveness-Implementation Trial to Evaluate a Sustainable, Peer-Delivered Intervention for Depression and Substance Use in a Low-Resource, Underserved Setting - Individuals from financially limited communities have limited access to evidence-based interventions (EBIs) for mental health yet also experience greater psychiatric and medical comorbidities and poor treatment outcomes. Alarmingly, rates of major depressive disorder (MDD) and substance use disorder (SUD) have risen significantly for adults living in economic hardship over the past two decades, resulting in worsening clinical and functional outcomes. There is a pressing need to disseminate EBIs for MDD-SUD that are acceptable, scalable and sustainable in economically limited settings, including Certified Community Behavioral Health Clinics (CCBHCs) which seek to expand access to services in economically strained areas. Peer recovery specialists (PRSs), individuals in recovery from SUD, have promise for increasing access to EBIs and are widely employed in CCBHCs; yet, few studies have evaluated the clinical effectiveness, implementation, and cost-effectiveness of PRS-delivered EBIs, even as PRS models are rapidly scaling in the US. Preliminary data: PIs Felton and Magidson have led two open-label trials demonstrating the feasibility, acceptability, and preliminary effectiveness of a PRS-delivered model (Peer Activate) to improve MDD and SUD outcomes among economically-limited individuals. The team has shown that behavioral activation (BA), an EBI based on reinforcement theory and focused on scheduling of valued, adaptive behaviors is particularly suitable for PRS delivery and promising to address gaps in EBI access. Preliminary studies established the feasibility and acceptability of this approach; next steps are to conduct a large-scale randomized trial to evaluate clinical and cost effectiveness, test potential modifiable mechanisms of treatment effectiveness, and evaluate longer-term implementation. Methods: We propose to evaluate Peer Activate in a fully-powered randomized hybrid Type 1 effectiveness-implementation trial (n=250) in Detroit, MI. Leveraging a well-established partnership with a community-based, PRS-led CCBHC, we will compare Peer Activate to enhanced treatment as usual (ETAU; non-specific, PRS-delivered supportive care) on depressive symptoms (primary) and substance use (Aim 1), and evaluate potential mechanisms of this approach (environmental reward; Aim 2). Guided by the EPIS framework and Proctor’s model, we will evaluate longer-term implementation outcomes (Aim 3), including cost effectiveness. A community advisory board will guide all aspects of the trial to promote the potential for sustainability. Impact: Our proposal is consistent with the goals of PAR-21-130, NIMH strategic objectives to develop innovative service delivery models for economically limited individuals with mental health and SUD comorbidity, and NOT-MH-22-170 promotion of partnerships between academic institutions and CCBHCs. Findings have the potential to increase availability of sustainable EBIs for mental health and SUD comorbidity in hard-hit areas.