Ecological mHealth Cannabis Prevention for Youth Involved in the Juvenile Legal System - PROJECT SUMMARY/ABSTRACT An increasing number of youth involved in the legal system (YILS) use cannabis, which can lead to cannabis use disorder and associated legal, social, and educational impairment. Prevention of cannabis use disorder among YILS is rare and there are many barriers to successful implementation. Mobile health technology holds promise to identify ecological vulnerabilities for cannabis use among YILS and to intervene in their natural environment. Ecological Momentary Assessment/Intervention (EMA/EMI) have been effectively used with other populations to measure substance use and intervene in the natural environment. Additionally, individualized constellations of antecedents to substance use derived from EMA data have accurately predicted prospective use, suggesting that targeted, individualized EMI is a promising approach to prevent cannabis use disorder. The purpose of this mixed-methods K23 study is to 1) assess the feasibility, usability, and acceptability of using EMA to measure ecological antecedents to cannabis use, 2) co-develop and pilot test an EMI to deliver Personalized Feedback content to reduce cannabis use and prevent progression to cannabis use disorder among YILS, and then 3) evaluate the EMI’s preliminary efficacy to prevent cannabis use disorder among YILS who have initiated use. The overall goal of this application is to provide protected, mentored time to expand Dr. Evan Holloway’s (PI) capacity to become an independent health services researcher with expertise at the intersection of digital health, cannabis use, and health services interventions for YILS. Dr. Holloway will work with a team of experienced and knowledgeable mentors (Drs. Tolou-Shams, Borsari, Ling, Rizzo, & Santos) to develop expertise in EMA/EMI, cannabis use, secondary prevention of substance use, Personalized Feedback, and mobile health technologies, with youth involved in the legal system to support his achievement of these research and career goals. The proposed research study is a logical extension of Dr. Holloway’s program of research to date, which has focused on the complex interplay between behavioral health service delivery systems, individual, peer, family, and environmental influences on behavioral health and legal outcomes for YILS. This early career development award will provide the necessary candidate training and foundation for a larger R01 hybrid design clinical trial testing the efficacy of the mHealth EMI designed and tested during the K23, propelling a federally-funded program of research designed to prevent cannabis use disorder for YILS.