Abstract
<title>Abstract</title> <p> <bold>Purpose</bold> Preventing youth substance use and related harms is a global priority. Ecological momentary assessment (EMA) and ecological momentary interventions (EMIs), which assess and address substance use in real-time, may improve mechanistic understanding, screening, intervention in clinical care. This review synthesized EMA/EMI studies examining substance use among youth in clinical settings. <bold>Methods</bold> A systematic narrative review (PsychInfo, Medline Scopus) identified EMA/EMI studies assessing substance use in clinical samples of youth (mean/median age ≤ 25) across emergency, medical, mental health, and substance use treatment settings. <bold>Findings</bold> Of 12093 titles/abstracts and 2157 full texts, 43 studies of 24 unique protocols (15 observational, 9 intervention) were included. Alcohol (75%), cannabis (67%), and nicotine/tobacco (33%) were the most frequently studied substances. EMA protocols typically lasted 14 days with 4 daily prompts; 3 incorporated passive (bio)sensing. Studies included 270 momentary antecedents and 17 momentary consequences of substance use, organized into six domains: substance use, affect/cognitions, environmental context, social context, movement factors, and EMA compliance. Negative affect, contextual factors (e.g., evenings, weekends, friends), and prior substance use showed the most consistent associations with use, although findings were heterogeneous. Passive sensing approaches demonstrated strong predictive performance. Thirteen evaluated EMIs integrating real-time monitoring with feedback, goal-setting, and/or coping support reduced substance use harms. <bold>Conclusions</bold> EMA/EMI approaches show promise for understanding and addressing dynamic, context-dependents substance use processes among youth in clinical settings. While the evidence remains exploratory and methodologically heterogenous, findings suggest EMIs can deliver timely, individualized support. Future research should prioritize greater methodological transparency and rigor. </p>