PROJECT ABSTRACT The purpose of this timely and significant R34 proposal is to adapt an evidence-based posttraumatic stress disorder (PTSD) intervention for use among a polysubstance population receiving treatment for opioid use disorder in a methadone maintenance treatment (MMT) program. Polysubstance use of high-risk combinations, such as illicit opioids and stimulants, is a critical public health issue. Individuals who engage in these high-risk combinations are more likely to have histories of childhood trauma, multiple traumas, PTSD, and greater PTSD severity as compared to mono-substance using individuals. Trauma, co-morbid mental health disorders such as PTSD, and polysubstance use complicate treatment outcomes. This innovative pilot will use three aims to adapt an existing evidence-based PTSD intervention, Skills Training in Affective and Interpersonal Regulation with Narrative Therapy (STAIR-NT), via a massed treatment model (i.e., condensed treatment schedule) for patients in MMT who are engaged in illicit opioid-stimulant polysubstance use. The following aims are proposed: (1) to adapt the evidence-based intervention STAIR-NT for polysubstance use populations informed by the ADAPT-ITT framework, (2) to assess the feasibility and acceptability of the provisionally adapted STAIR-NT via an open pilot (n=10) to inform further adaptations, and (3) to conduct a small-scale randomized control pilot using the adapted intervention to examine implementation (i.e., feasibility and acceptability) and short-term polysubstance use and PTSD symptomology outcomes among MMT patients who are engaged in illicit opioid-stimulant polysubstance use. Completion of study aims will result in a fully adapted protocol for use in a multi-site randomized trial of the adapted STAIR-NT approach. The long-term goal of this research is to improve the health and treatment outcomes of populations who engage in high-risk polysubstance use through complementary layering of trauma-informed evidence-based interventions in opioid treatment programs.