A Randomized Controlled Trial of A Smartphone Delivered Treatment for Suicidal Thoughts and Behavior - Modified Project Summary/Abstract Section Suicidal thoughts and behavior (STB) claim nearly 50,000 Americans and contribute >$90 billion in disease burden annually. Existing STB treatments cannot address the enormity of this problem because they are not scalable. Recent research shows that low aversion to suicide (i.e., perceiving it as less negative) is a STB risk factor and promising treatment target. However, no study has examined whether increasing suicide-aversion (making suicide seem worse) reduces STB. This K23 project follows an experimental therapeutic approach to answer this question. We will conduct user-centered design interviews with five adults (18+) and a one-arm open trial with 20 adults with recent and frequent STB residing within ~50 miles of Boston, MA to evaluate the safety and acceptability of Therapeutic Evaluative Condition for Suicide (TEC-S). TEC-S is a classical conditioning-based intervention delivered via smartphone targeting suicide-aversion. Based on these safety and acceptability data, we will optimize TEC-S (e.g., select specific stimuli) and randomize 60 adults with recent/frequent STB in the Boston area to receive 30 days of either active- or inactive Therapeutic Evaluative Condition for Suicide (TEC-S). We predict that active vs. inactive TEC-S will be associated with increased suicide-aversion (primary target) over the 30- day treatment period, as assessed weekly via self-report and behavioral assay. Also, we predict that active vs. inactive TEC-S will be associated with reduced STB severity (e.g., suicidal desire) and incidence (e.g., suicide plans, attempts) during treatment, and that increases in suicide-aversion will be associated with these STB reductions (target validation). STB outcomes will be measured via ecological momentary assessment (EMA) three times per day during the 30-day treatment period, and once daily during a subsequent 30-day follow up. This project will produce the data required to develop an R-level optimization trial testing TEC-S among higherrisk suicidal participants leaving inpatient care. Study aims perfectly align with the candidate’s training goals: (1) conduct an RCT for STB delivered via smartphone; (2) design and implement EMA to measure STB; (3) ethics and human subjects protections in EMA with suicidal participants; (4) advanced statistics for multilevel, longitudinal data, including mediation and sensitivity analyses; and (5) career development. These training goals will be accomplished through the expert mentorship and guidance of the candidate’s primary mentor Dr. Sabine Wilhelm (RCT and digital mental health expert), co-mentor Dr. Evan Kleiman (STB EMA expert), ethics and safety advisor Dr. Kate Bentley (ethics and safety/risk management in STB expert), statistical advisor Dr. Walter Dempsey (longitudinal and mobile health statistical expert), and technical advisor Dr. Alex Millner (STB and TEC expert). If successful, this project could establish an evidence base for a highly scalable, costeffective, and mechanistically informed STB treatment that could prevent the tragic loss of life caused by STB. The proposed project and training plan provide unparalleled learning/growth opportunities, launching the candidate’s independent research career focused on developing and testing scalable STB treatments.