Longitudinal Emergence of Concurrent Mental Health and Substance Use Concerns in an Ontario School-Based Sample: The Research and Action for Teens Study.

Objectives This study characterizes patterns of mental health, substance use and their co-occurrence, and identifies developmental trajectories associated with progression from single to concurrent mental health and substance use concerns in an Ontario school-based population. It is a longitudinal extension of the Ontario Student Drug Use and Mental Health Survey, as part of the RAFT collaborative project. Methods In this study, an Ontario-wide survey was administered to students across three biennial waves starting in grades 7-8 (ages 12-14). We explored how developmental patterns of externalizing, internalizing and co-occurring symptoms were differentially associated with late-adolescent (ages 17-19) problematic substance use. Results On average, students exhibited early (ages 12-14) moderate risk of an internalizing and/or externalizing disorder and approached the low threshold for a diagnostic concern for substance use disorder at age 17-19. The pattern confirmed a potential pathway from early mental health concerns to later adolescent problematic substance use, with rates of co-occurrence increasing with age. Youth with early moderate-to high externalizing and co-occurring internalizing and externalizing symptomology had the highest levels of problematic substance use, with scores indicating high likelihood of a substance use disorder diagnosis. Conclusions Given the overall pattern of progression, early identification and referral of at-risk youth, especially youth with co-occurring mental health concerns, is of critical importance. Findings support the importance of integrated and co-located mental health and substance use services for youth to more effectively serve a diverse population of youth with varying levels of need.