CHARACTERIZING THE CO-OCCURRENCE OF SUBSTANCE USE AND MENTAL HEALTH SYMPTOMS AMONG ADOLESCENTS IN GENERAL POPULATION AND CLINICAL SAMPLES

Background: Despite policy and practice guidelines highlighting the need to identify and treat substance use early and concurrently with other mental health symptoms, efforts remain uncoordinated and guidelines lack specificity. Limited evidence characterizing patterns and correlates of co-occurring substance use and mental health symptoms hinders our ability to effectively address these concerns early during adolescence. This dissertation deepens our understanding of the patterns and correlates of co-occurring substance use and mental health symptoms among adolescents, how to collect relevant data in inpatient settings, and how to rigorously analyze and report findings. Methods: The first paper is a systematic review of 70 cluster-based studies examining patterns of multiple substance use among adolescents. The second examines patterns and correlates of co-occurring substance use and mental health symptoms through multilevel latent profile analysis and multilevel multinomial regression using a large, representative sample of secondary students and schools across Ontario. The third paper is a pilot study examining the feasibility, acceptability, and importance of standardized assessments of substance use and mental health symptoms in an adolescent psychiatric inpatient unit. Results: The substantive findings of this work include: 1) multiple substance use is common; 2) co-occurrence of substance use and mental health symptoms is common, though not universal; 3) substance use may be related to mental health symptom severity, comorbidity, and hospital service use; 4) school climate, belonging, and safety represent important targets for school-based interventions; and 5) adolescent psychiatric inpatient units may represent important contexts for standardized assessments, though more professional training and standardization in assessments and interventions are needed. Methodological recommendations are also presented to improve the collection, analysis, and reporting of similar work in the field. Conclusions: Collectively, this dissertation provides novel, timely, and actionable insight into adolescent substance use patterns, correlates, and potential targets for assessment and intervention efforts. Dissertation Doctor of Philosophy (PhD) This dissertation deepens our understanding of the patterns of co-occurring substance use and mental health concerns among adolescents. First, a review of all existing studies that explore patterns of multiple substance use among adolescents was conducted. Second, patterns of substance use and mental health symptoms were identified in secondary students and schools across Ontario. Third, the feasibility of assessing substance use and mental health symptoms using standardized approaches on an inpatient adolescent psychiatric unit was evaluated. Overall, this work suggests that substance use and mental health concerns commonly co-occur, and that schools and inpatient psychiatric units are important settings for prevention, assessment, and intervention. This work provides actionable next steps to inform assessment, prevention, and intervention efforts designed to address co-occurring substance use and mental health concerns among adolescents.