Project Summary/Abstract Posttraumatic stress disorder (PTSD) is a debilitating psychiatric disorder that affects 6% of U.S. adults, yet is left untreated in 70% of affected individuals and up to 85% of low-income individuals. One third of the nation’s low-income individuals are treated in Federally Qualified Health Centers (FQHCs), which do not have the capacity to provide all their patients with first-line, evidence-based treatments for PTSD such as Prolonged Exposure (PE). To address this problem, the study team has developed a low-intensity intervention (PTSD Coach) and a medium-intensity intervention (PE for Primary Care: PE-PC) that effectively treat PTSD in low- resource settings. However, some patients will still require high-intensity treatments (e.g., Full PE) for sustained clinical benefit. Thus, there is a critical need to develop adaptive, stepped-care models to treat PTSD in FQHCs by combining efficacious treatments, based on response to initial lower-cost strategies. The long- term goal of this line of research is to improve access to efficacious PTSD treatments by implementing empirically-based stepped-care behavioral interventions in low-resource domestic settings. The overall objective in this proposal is to develop a stepped-care intervention for PTSD using a Sequential, Multiple Assignment, Randomized Trial (SMART). The central hypothesis is that beginning with a low- or medium- intensity PTSD intervention and then titrating intensity based on early indications of response will result in clinically-significant PTSD symptom reduction with parsimony of resources. The rationale is that stepped-care interventions for PTSD are scalable and less costly than static treatments, thereby improving efficiency. To accomplish the objective, this project will employ a SMART design with 430 adults with PTSD in six FQHCs. Participants will be initially randomized to PTSD Coach or PE-PC. After four weeks, early responders will step down to lower frequency interaction within their current treatment strategy. Slow responders will be re- randomized to either continue their current treatment strategy or step up to Full PE for eight weeks. The specific aims are to: (1) Test the effectiveness of initiating treatment with PE-PC versus PTSD Coach in reducing PTSD symptoms at 3 months (endpoint), 6-month follow-up and 9-month follow-up, and (2) Test the effectiveness of second-stage tactics (continue or step up to Full PE) for slow responders. Exploratory aims are to (A) Identify the optimal stepped-care treatment sequence; (B) Conduct cost-effectiveness analysis; (C) Identify key mediators/moderators of treatment response; and (D) Prepare for future implementation through process evaluation. This project will contribute to the field an empirically-based stepped-care intervention for PTSD. This contribution is significant because it will improve clinical practice for PTSD by establishing an effective treatment sequence that can be delivered in a scalab...