Basic History Siddha Medicine:

According to tradition, there were 18 Siddhars (the person who has achieved some extra-ordinary powers but the Agasthiyar (Agastya) was the topmost. He is regarded as the originator of the Siddha medicine and also of the Tamil language. He occupies the same position as Hippocrates in modern western medicine. In the period of Ramayana he seems to have settled in the South. Thus origin of every tradition in the South, including language and culture, is traced back to Agastya.

The Maha Sidha Agastiya, an Enlighted Master and Healer in "Cittar Medicine"( The Science of Mind )"

The word Siddha denotes one who has achieved some extraordinary powers (siddhi). This achievement was related to the discipline of mind and its superiority over body, and was accomplished through both yoga and medicine. Thus siddhars (practitioners of Siddha) became the symbols of psychosomatic perfection and so the Siddha medicine became a combination of medicine and yoga.
According to the Siddha medicine various psychological and physiological functions of the body are attributed to the combination of seven elements: first is saram (plasma) responsible for growth, development and nourishment; second is cheneer (blood) responsible for nourishing muscles, imparting colour and improving intellect; the third is ooun (muscle) responsible for shape of the body; fourth is kollzuppu (fatty tissue) responsible for oil balance and lubricating joints; fifth is enbu (bone) responsible for body structure and posture and movement; sixth is moolai (nerve) responsible for strength; and the last is sukila (semen) responsible for reproduction. Like in Ayurveda, in Siddha medicine also the physiological components of the human beings are classified as Vatha (air), Pitha (fire) and Kapha (earth and water). In Siddha medicine the use of metals and minerals are more predominant in comparison to other Indian traditional medicine systems. In the usage of metals, minerals and other chemicals, this system was far more advanced than Ayurveda.
When the normal equilibrium of three humors (vatha, pitha and kapha) is disturbed, disease is caused. The factors, which affect this equilibrium are environment, climatic conditions, diet, physical activities, and stress. Under normal conditions, the ratio between these three humors (vatha, pitha and kapha) is 4:2:1 respectively.
According to the Siddha medicine system diet and life style play a major role not only in health but also in curing diseases. This concept of the Siddha medicine is termed as pathya and apathya, which is essentially a list of do's and dont's.