Supporting Treatment Access and Recovery in Re-entry (STAR-R) - Individuals with substance use and mental health conditions (COD) are overrepresented in criminal legal (CL) settings, including jails with 50% having a COD. Compared to having a single disorder, those with a COD have more serious criminal histories, adverse childhood experiences, reincarceration, suicide, homelessness, unemployment, poor treatment engagement, and a tenfold increased risk of overdosing within 3 months of release. While treatments exist to address mental health, substance use, CL prosocial thinking, and social service needs separately, there is an absence of comprehensive re-entry approaches that address these needs simultaneously, which can result in care fragmentation, poor treatment engagement, relapses, and a vicious cycle of reincarceration. Maintaining Independence and Sobriety through Systems Integration, Outreach, and Networking-Criminal Justice version (MISSION-CJ) is a promising, cross-disciplinary multicomponent intervention, offering 6 months of COD treatment, prosocial and recovery services, and assertive outreach. Four MISSION-CJ open pilots demonstrated increased treatment engagement, improved behavioral health outcomes, and reduced recidivism for clients with a COD. We also have a MISSION-CJ Manual, Workbook, Treatment Planning Tool, and Fidelity Measure and are ready to test them in this RCT. In response to RFA-DA-25-062, the proposed 5-year study, “Supporting Treatment Access and Recovery in Re-entry (STAR-R),” will randomize 240 people with COD to MISSION-CJ or Peer Linkage Support (PLS). Study aims include Aim 1: Compared to PLS, those receiving MISSION-CJ are hypothesized to show: (1a) greater engagement in treatment (measured by total days participated in each condition), and total community provider linkages sessions); (1b) Reduced substance use (measured by self-report use days); reduced overdose risk (measured by self-report Overdose Risk Questionnaire) / overdoses (self-report and corroborated with surveillance data); and reduced mental health symptoms (measured by self-report mental health symptoms); (1c) less CL recidivism (measured by fewer days in jail and fewer numbers of arrests). Aim 2: Examine mechanisms impacting Aim 1 outcomes. Treatment effects will be mediated by: (i) recidivism risk; (ii) increased affiliations with prosocial peers; (iii) reduced affiliations with antisocial peers; and (iv) increased community integration; and will be moderated by demographic factors and COD severity. Aim 3: To conduct a comprehensive economic evaluation that will (i) estimate the full implementation (start-up and ongoing) costs associated with MISSION-CJ and PLS, and (ii) evaluate the cost-effectiveness of MISSION-CJ compared to PLS, from the healthcare system and societal perspectives. Aim 4. To examine facilitators and challenges of MISSION-CJ implementation via qualitative interviews with participants (n=20) and staff (N=12). This application is responsive to NIDA priorities by proposing to improve treatment within the CL system, and to optimize continuity of care post incarceration, and the JCOIN goals of addressing the intersection of the CL system and the community-based healthcare system. This study is part of the NIH’s Helping to End Addiction Long-term (HEAL) initiative to speed scientific solutions to the national opioid public health crisis. The NIH HEAL Initiative bolsters research across NIH to improve treatment for opioid misuse and addiction.