PROJECT SUMMARY Opiate use and overdose deaths have been rising, especially during COVID. Youth involved with the legal system (YILS) have some of the highest rates of opioid use disorder (OUD); local rates in the Washington State Juvenile Rehabilitation (WSJR) system approach 1 in 3 youth. Nationwide, most YILS engage in problematic non-opioid substance use, a critical risk factor for OUD. Non-opioid substance use disorders (SUDs) and OUDs, in turn, are two of the most important predictors of subsequent re-involvement in juvenile or criminal systems. In a 5-year UG3/UH3 grant, Seattle Children’s Hospital (SCH), University of Washington (UW), and WSJR are collaboratively evaluating OUD prevention interventions of varying intensities based on the Adolescent Community Reinforcement Approach with Assertive Continuing Care (ACRA/ACC). Multiple studies have established ACRA/ACC effectiveness in reducing SUD; however, none have evaluated it as OUD prevention. We are using SMART methods to construct ahigh-quality adaptive intervention (AI) containing ACRA/ACC- based OUD prevention strategies of two different intensities. In our 2-year UG3 phase, we conducted a pilot SMART experiment with 31 YILS. In our 3-year UH3 phase, we are conducting a full SMART trial with YILS aged 15-25 to compared effects of our prevention interventions during the following stages: a) as youth transition out of confinement (stage 1), and b) once they are back in the community (stage 2). We administer self-report electronic surveys at baseline, 1, 3, & 6 months to collect data on primary outcomes (initiation and escalation of use measured by number of days and frequency of use of any substances) and secondary outcomes (number of days/ frequency of use of specific substances including opioids); we will use administrative data to measure recidivism. We are also conducting comprehensive cost analyses. Currently, we have achieved recruitment and retention rates that exceeded our goals as written in the parent grant (72% and 76%). However, due to increasing OUD rates resulting in a smaller proportion of current WSJR YILS qualifying for inclusion in this opioid prevention trial, longer average sentence lengths, and COVID reductions in census, we are recruiting at ~half of the weekly rate we originally anticipated. At the current rates, 187 youth will finish the study. This will allow us to assess stage 1 intervention effects on primary outcomes but could limit our ability to assess stage 1 effects on some secondary outcomes or stage 2 effects. In the present administrative supplement, we seek to mitigate COVID effects on sample size via increased incentives, increased budget for food rewards (which are a standard part of ACRA/ACC), as well as increases in recruiter/surveyor and interventionist FTEs. We seek to boost both recruitment and retention rates to 85%, which will allow us to enroll and retain at least 292 and 248 YILS, respectively. These added participants will increase our p...