IMPORTANCE: Adolescent cannabis use is a substantial public health concern given its associations with adverse mental and physical health outcomes. Understanding how distinct use patterns are associated with medical care utilization in young adulthood is critical for prevention.

OBJECTIVE: To examine the association between patterns of adolescent cannabis use and medical care utilization for mental and physical health conditions in young adulthood.

DESIGN, SETTING, AND PARTICIPANTS: This population-based birth cohort study linked to population-wide administrative medical care databases was conducted in the Province of Québec, Canada. Participants included individuals recruited for the Québec Longitudinal Study of Child Development, followed up from birth (1997-1998) to 23 years of age (2021). Data were analyzed November 2023 to February 2025.

EXPOSURE: Self-reported past 12-month cannabis use at ages 12, 13, 15, and 17 years.

MAIN OUTCOMES AND MEASURES: Medical care utilization for any mental disorder (including common mental disorders and substance-related disorders), suicide-related behaviors, and any physical health condition (including respiratory diseases, injuries and poisoning, and other physical diseases) between ages 18 and 23 years. Analyses were adjusted for 32 individual, family, and community-level confounders measured from birth to younger than 12 years of age using overlap weights.

RESULTS: Data for 1591 individuals (818 female [51.4%]; mean [SD] age at first exposure assessment, 12.1 [0.3] years) were analyzed. Three distinct adolescent cannabis use patterns were identified via group-based trajectory modeling: nonuse (948 [59.6%]), late-onset use (318 [20.0%], initiating after age 15 years), and early-onset and frequent use (325 [20.4%], initiating before age 15 years). In fully adjusted analyses, individuals with early-onset and frequent use had significantly higher odds of medical care utilization for any mental disorder (odds ratio [OR], 1.51 [95% CI, 1.10-2.08]), common mental disorders (OR, 1.57 [95% CI, 1.12-2.21]), any physical health condition (OR, 1.86 [95% CI, 1.30-2.67]), injuries and poisoning (OR, 1.41 [1.05-1.89]), and other physical diseases (OR, 1.47 [95% CI, 1.08-1.98]), compared with individuals with no use. Individuals with late-onset use did not differ significantly from those with nonuse for mental health outcomes (OR, 1.13 [95% CI, 0.80-1.58]) but had higher odds of medical care utilization for any physical health condition (OR, 1.63 [95% CI, 1.16-2.28]).

CONCLUSIONS AND RELEVANCE: Findings of this birth cohort study indicated that early-onset and frequent cannabis use was associated with greater medical care utilization for both mental and physical health conditions in young adulthood. These findings support the relevance of delaying initiation and reducing intensity of cannabis use during adolescence.