About half of individuals in the justice system who use opioids have a co-occurring mental health disorder, and the transition from jail to the community is a vulnerable period with a three-to-eight-fold increased risk of post-release overdose. Those released from jail have difficulty accessing treatment and addressing social determinants of health needs (SDOH). While evidence-based reentry services link individuals being released from jail to community-based behavioral health treatments and other social services, they fall short in providing “on-demand,” 24/7 support during this vulnerable period. This R41 STTR aims to develop and test a prototype mobile health application (mHealth app) called R- Assist to support individuals released from jail in their recovery from co-occurring opioid use and mental health disorders (henceforth called COD) via a partnership between the University of Massachusetts (UMass), with expertise in COD interventions for criminal justice populations and computer science, and Meaningful Measurement, a women owned small business with 25 years of healthcare experience. To offer support during this vulnerable post-release care period, we propose to build and establish technical merit and feasibility of Reentry-Assist (R-Assist), the first client facing, low cost, stand-alone mHealth app (iOS and Android; and compatible with tablets) for individuals with a COD releasing from jail. Individuals with lived criminal justice experience, staff working in the field, and the developers with collectively over 50 years of experience in care coordination, COD treatment, and digital health solutions have all worked together in conceptualizing R-Assist The following Aims will be tested. Aim 1. R-Assist software and content prototype development. The 4 R-Assist features will include: 1) daily self-reported symptom and medication management monitoring; 2) a 29-session MISSION-CJ self-help curriculum, with an accompanying library of recovery resources to support COD symptom management and promote prosocial thinking and behavior; 3) SDH resource finder; and 4) a dashboard to track R-Assist engagement. In Phase II we will build a Virtual Reentry Support Assistant to enhance the user experience, and all powered by Artificial Intelligence (AI) for a customizable experience. Aim 2. Successive cohort study of the R-Assist prototype with clients leaving jail (N = 38). This will include three successive field focus group cohorts with 18 clients, followed by a small open pilot with 20 clients. This will all be done in preparation for a larger Phase II trial. This project proposes a next generation mHealth app that specifically targets the transition from jail to the community and helps empower clients towards a path of recovery. R-Assist is in line with the goals of NIDA RFA DA-24-017, i.e., developing “low- cost technologies specifically tailored to increase access to treatment in correctional facilities, poor and rural communities, as well as in...