Zonisamide is a sulfonamide drug used primarily for the treatment of partial seizures in adults. We describe the case of a 15-year-old woman with a mood disorder who survived without complications after ingestion of an estimated 7.5 g of zonisamide. To the best of our knowledge, there are 4 case reports of individuals with intentional ingestion of more than 4 g of zonisamide as a single agent. Our patient developed coma and hypotension 4 hours after ingestion and was treated with a catecholamine infusion, endotracheal intubation, and mechanical ventilation. She had mild electrocardiographic abnormalities and fully recovered after 4 days. This report contributes to the understanding of acute zonisamide poisoning.