WHY IT MATTERS: If you are a parent, caregiver, or young adult considering cannabis, this study reinforces that adolescent brain development is a critical window where unsupervised use may carry serious long-term psychiatric risks that do not necessarily apply to adult medical patients under clinical guidance. CLINICAL OVERVIEW: A new longitudinal study links adolescent cannabis use to increased risk of later bipolar and psychotic disorder diagnoses, adding to a growing body of evidence that the developing brain is uniquely vulnerable to cannabinoid exposure. While this research does not apply directly to adult medical cannabis patients, it reinforces what clinicians in cannabis medicine have long emphasized: age of onset matters enormously, and adolescent use carries a fundamentally different risk profile than supervised adult medical use.