The purpose of the Treatment for Harnessing Resiliency, Improving emotional regulation, and empowering indiViduals for a brighter future (THRIVE) study is to adapt an evidence-based posttraumatic stress disorder (PTSD) treatment for use among a polysubstance population receiving methadone maintenance treatment (MMT) at an opioid treatment 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 study will use eight study phases 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 sustained opioid-stimulant polysubstance use. The intervention is an adapted version of the STAIR-NT protocol. The massed version created includes four 60-min sessions of skill building and two weeks of four 60-min sessions of narrative therapy. A preliminary randomized controlled trial (RCT) with 80 participants, randomized 1:1, will be conducted to assess the intervention's implementation and impact on primary short-term outcomes of polysubstance use and PTSD symptoms. The results of this study will inform a fully-powered effectiveness trial for individuals with PTSD and polysubstance use receiving MMT. The findings are expected to provide valuable insights into improving both PTSD and substance use outcomes, and real-world implementation insights to integrating trauma-informed care in treatment settings for vulnerable populations. This study is registered at ClinicalTrials.Gov as NCT06307340. Registration date 03/2024.