In the course of time, Ayurveda prevalent in the north supplemented itself and also enriched the Siddha system of medicine prevalent in the south. The latter’s origin is attributed to sage Agasthya and ancient texts mention 18 Siddhars or seers of knowledge as the initial proponents of this system. The therapeutics of Siddha medicine, an ocean of knowledge by itself, consisted mainly of the use of metals, minerals and ores including mercury, arsenic, mica, magnetic iron, gold, silver, antimony etc. Well versed in alchemy, ancient Siddha practitioners knew the medicinal uses of metallic compounds and ores and were adept in the preparation of medicines from these which unlike vegetable drugs are not subject to decay and do not lose potency over time. These medicines administered in small doses and available at all seasons could be well preserved. According to Siddha percepts, which shared the same panchabhautic concept of the human body with Ayurveda, metal-based drugs could arrest the decay of the human body. This, the ancient forerunner of Rasayana therapy, possibly influenced the development of Rasachikitsa referring to the collection of treatment practices under the Rasayana or rejuvenative therapy of Ayurveda. It employed metals, their salts and alloys and also sulphurs. Works devoted to the preparation of inorganic and metallic remedies are among the most prolific and rewarding sources of knowledge of ancient Indian chemistry. The Rasachikitsa school of medicine has been a rival of Ayurveda in popularity and prestige during many centuries in the past especially in south India, eastern provinces and Sind. It survives to the present day as a living system of medicine and has absorbed many tenets of classic Ayurveda.