Preventing Substance Use Among Youth in Foster Care Through Collaborative Court Appointed Special Advocates(CASA) Brief Intervention - 7. Project Summary/Abstract Research documents that youth in foster care exhibit elevated risk for substance use problems compared to the general adolescent population. Yet substance use prevention programs often fail to reach youth in foster care due to a number of factors, including high rates of placement instability, a critical lack of substance use programming tailored for the unique needs of youth in foster care, and implementation challenges. Increasing referrals is not an effective strategy alone, and substance use prevention is not part of services as usual for youth in foster care. The objective of this R01 is to leverage a robust existing service delivery program for youth in foster care, Court Appointed Special Advocates (CASAs), to deliver an evidence-based intervention (EBI) specifically focused on trauma-informed substance use prevention, called CASA Brief Intervention (CBI). We will first adapt core components of existing EBIs so that they are tailored for the needs of youth in foster care and can be delivered by CASAs (Aim 1). We will then conduct a large-scale hybrid type 1 effectiveness- implementation randomized trial to test whether the adapted intervention improves substance use outcomes for foster youth compared to CASA services-as-usual (Aim 2 and Aim 3). CASAs are ideal interventionists for youth in foster care because the structure for hiring, training, and monitoring CASAs to support youth in foster care already exists nationwide. In this proposal, we build on an existing partnership between the University of Oregon, CASA of Lane County, and the joint CASA program of Josephine and Jackson Counties. The overall goal of this project is to expand our current partnership with CASA to co-adapt and deliver effective substance use programming to youth in foster care. Findings will clarify the implications of using a lay health worker model to improve the implementation, sustainability, and scalability of substance use prevention programming for youth in foster care. Given that CASA is currently in 49 U.S. states, serving approximately 242,000 (60%) youth in foster care, the potential for scalability and reach is exceptional if the current project demonstrates that the EBI delivered by CASAs effectively prevents substance use and improves outcomes for youth foster youth.