PROJECT SUMMARY The increasing rates of suicide among adolescents is an urgent public health concern. In parallel, acute services due to suicide risk, including psychiatric hospitalizations, have been on the rise, with discharged adolescents remaining at elevated risk for recurrent suicidal crises. New approaches are urgently needed to alter risk trajectories and prevent suicidal behavior among adolescents transitioning from inpatient care. Bridging an adaptive intervention (AI) approach—wherein type, intensity, and timing of treatment can be individualized to address suicidal adolescents’ heterogenous treatment needs—together with technology- augmented follow-up support provided during the high-risk transition period, this study seeks to identify an effective AI for reducing youth suicidal behavior after inpatient care. In our ongoing full-scale sequential multiple assignment randomized trial (SMART) of a multi-component intervention—i.e. incorporating a Motivational Interview (MI)-enhanced safety plan delivered during hospitalization (MI-SP) and post-discharge supportive contacts provided via a booster call, asynchronous portal, or text messages (Texts)—hospitalized adolescents (N=300) at risk for suicide are initially randomized to MI-SP or to MI-SP with Texts, and those classified as non-responders within 2 weeks post discharge are re-randomized to an added booster call or portal conditions. The R01 SMART was funded to determine the effectiveness of promising technology- augmented intervention strategies and their sequencing, including comparing four AIs embedded in the SMART, on the primary outcome of suicidal behavior (actual, interrupted, aborted attempts) within 3 months post discharge and secondary outcomes of time-to-suicidal behavior and suicidal ideation severity over 6 months. In secondary analyses, we plan to investigate moderators of intervention strategies, examine proposed mechanisms of action, and identify barriers and facilitators to implementation. The trial was successfully launched across two health system sites; however the overall rate of recruitment across both sites has been lower than expected, and further compounded by lower number of admissions at one of the sites. To address these challenges and enrollment shortfalls that would limit the study’s statistical power to determine the effectiveness and optimal sequence of different intervention strategies on the primary outcome of suicidal behavior, we recently added an additional recruitment site–Cincinnati Children’s Hospital and Medical Center (CCHMC). CCMHC was selected due to its relatively large child/adolescent inpatient program and diverse patient population (~30% Black youth). We have made important study launch gains at CCHM, including completing regulatory and study startup steps and staff training, with trial enrollment beginning midway through Year 3. This supplement will enable completing enrollment and associated intervention and follow-up activities at CCH...