Abstract
Objective: Opioid-related harms in Canada have escalated over the past decade, yet little is known about current substance use pathways among adults seeking support for substance use. Most clinical measures focus on current symptoms rather than sequencing or timing of substance use initiation. This study addresses this gap by examining patterns of substance initiations, timing, and progression in a large clinical sample seeking substance use treatment at the Center for Addiction and Mental Health (CAMH). Method: Participants (N = 200) completed a survey of substance use over the lifespan alongside measures of opioid use disorder (OUD) symptoms, substance-related consequences, and treatment history. Analyses included Cox proportional hazard models predicting opioid initiation, and latent class analysis (LCA) to identify substance initiation profiles. Results: Alcohol (90.5%), cannabis (71.5%), and tobacco (58.5%) were the most commonly used and earliest initiated substances. Lifetime opioid use was reported by 63.5% of participants, with 40.5% endorsing ≥2 OUD symptoms. Individuals with OUD symptoms initiated alcohol, cannabis, and tobacco at earlier ages (p Conclusions: Adult substance use pathways among individuals seeking treatment are diverse. Early initiation of cannabis and tobacco were associated with opioid involvement. Pathways-based assessment and early intervention may strengthen prevention, harm reduction, and treatment strategies.