Isoniazid (INH) is widely used in most prophylactic and therapeutic anti-tuberculosis regimens because of its effectiveness and low cost. Yet, INH poisoning appears to be rare. We report the first case of intentional INH overdosage in Singapore. A 26-year-old Filipino male presented with mental obtundation, recurrent seizures, metabolic acidosis and hepatic dysfunction. He was successfully treated with large doses of pyridoxine (vitamin B6). Recommendations for the management of acute INH toxicity are highlighted.