Siddha is one of the oldest system of medicine practiced in India. This system was developed in the state of Tamil Nadu in India. It is supposed to have been conceived by the Siddhas or evolved souls ( numbering 18) who lived in the past. The word 'Siddha' comes from 'Siddhi' which means an object to be attained or perfection of heavenly bliss.

Siddhas or Siddhars were great doctors of medicine, philosophers, men with deep knowledge of anatomy and chemistry and savants noted for their wide travel, simple living and high thinking. The Siddhas have their own manuscripts or basic works, written in secret code. Some of the  treasured treatises on medicine are poems in palm leaf manuscripts which are now preserved in the Saraswathi Mahal Library, Tanjavur in Tamil Nadu. They were the pioneers in the use of metals and minerals in the treatment of diseases.

The systems of Siddha and Ayurveda are very much similar. In both systems, the basis of treatment is the three element theory or 'tridosha' (three humours). The three humours are Vatha (air), Pitta (bile) and Kapha (phlegm). It is believed that without these humours an individual cannot exist and imbalance of these may cause diseases. There are number of medicines common to both Siddha and Ayurveda. In both systems medicines are prescribed to set right the imbalance in the three life factors.

In Siddha, diseases are diagnosed mainly with the help of signs and symptoms of diseases. Other factors that help to diagnose diseases are touch, examining the pulse, tongue, colour, speech, eyes, faeces and urine. 

The main aim of Siddha is to assure a healthy life to man kind.