WHY IT MATTERS: Parents and adolescent patients should understand that the psychiatric risks associated with cannabis use before age 18 are biologically distinct from adult-onset use, and delaying initiation until adulthood is one of the most evidence-supported harm reduction strategies available. CLINICAL OVERVIEW: Research examining adolescent cannabis use has consistently identified a meaningful association between early initiation and elevated risk for psychotic spectrum disorders in adulthood, with the biological vulnerability of the developing adolescent brain playing a central role in this relationship. The endocannabinoid system undergoes significant maturation throughout adolescence, and exogenous cannabinoids introduced during this window appear to disrupt neurodevelopmental trajectories in ways that can have lasting psychiatric consequences.