Previous research has identified pesticides as the commonest substance used in poisoning in Sri Lanka. The aim of the study is to describe substances used in overdose and the characteristics of patients admitted with medicinal drug overdose in an urban tertiary care hospital in Colombo. A descriptive study of one hundred and ninety one patients admitted with intentional self poisoning to National Hospital of Sri Lanka, Colombo was carried out. Medicinal drugs were the commonest substance used in overdose (68%). Those who used medicinal drugs were mainly female (72.3%) and were aged between 15-24 years (76.2%). In Colombo medicinal drugs were the commonest substance used in intentional self poisoning in contrast to findings in rural areas.