Case Report: Intentional massive melatonin ingestion (450 mg) in an adolescent female

Over-the-counter (OTC) melatonin is widely perceived as benign, yet its unregulated, high-dose formulations create an accessible means of self-harm for adolescents, and reports of intentional overdose have risen alongside a well-documented surge in pediatric exposures. We report a 16-year-old female who intentionally ingested 450 mg of melatonin (90 × 5 mg tablets), a 90-fold supratherapeutic dose, and synthesize this case against the published literature on melatonin overdose, suicidality, and toxicokinetics. She presented 2.5 h post-ingestion with marked somnolence (Glasgow Coma Scale 13/15) and heart rate of 62 beats/min. Venous blood gas showed a mild, respiratory-compensated metabolic acidosis (pH 7.34, HCO3 15.6 mmol/L), with mild hyponatremia and stress leukocytosis. Hepatic, renal, and coagulation studies and a 12-lead electrocardiogram were normal, and a comprehensive toxicology screen was negative, consistent with an isolated exposure (Poison Severity Score Grade 1, Minor). She was medically cleared within 14.5 h of ingestion but, given persistent suicidal ideation on psychiatric evaluation, was transferred to inpatient psychiatric care at 20.5 h post-ingestion. This case, together with a review of published case reports, cohort data, and toxicokinetic evidence, indicates that massive isolated melatonin ingestion typically produces self-limited sedation, consistent with saturable hepatic CYP1A2-mediated clearance, alongside mild, transient metabolic derangement without organ injury. Population-level and case-level evidence converge, however, on a critical message for clinicians: low physiological toxicity does not indicate low psychiatric risk, and every adolescent presenting after intentional OTC chronobiotic ingestion warrants formal psychiatric evaluation regardless of how benign the medical course appears.