Siddha system is one of the oldest systems of medicine in India. This principles and doctrines of this system, both fundamental and applied, have a close similarity to Ayurveda, with specialization in iatrochemistry. The drugs used by the Siddhars could be classified into three groups: herbal product, inorganic substances and animal products. The Siddha Medicines which contains mercury, silver, arsenic, lead and sulfur have been found to be effective in treating certain infectious diseases. Sidha system is not recognized in several countries because of the lack of research proving the safety of mineral & metallic preparations. According to the Siddha medicine system, diet and lifestyle play a major role in health and in curing diseases.