This system of medical practice is associated wit the Tamil speaking parts
of India.
The term Siddha is derived from Siddha, which means attainment of perfection.
The origin of this system of medicine is associated with the desire of saints who relentlessly took efforts to attain salvation.
These saints realised that a good physical body free from disease was required to attain eternal bliss. They evolved a system of medicine primarily for the healthy living and also for the elimination of disease. This traditional Tamil system was refined by Saivite saints called siddhars. It's also known as Agastya after it's famous exponent, sage Agastya.
Like all the traditional India medicines, siddha is based on body humours and other characteristics similar to those in Ayurveda. According to siddha system, the universe consists of 5 elements -- earth, water, fire, air and ether that correspond to the five senses of the human body. A suitable proportion of these 5 elements in combination with each other produce a healthy person.
Mercury and sulphur play a major role in the therapeutics of this medical science and often, they are used in combination. Siddha medicine has an interesting way of categorizing drugs. On the basis of mutual interaction the drugs are called enemies or friends based on the compatibility with each other.
The Siddha practitioner considers these aspects while administering the drugs. The diagnosis in siddha is based on findings from eight aspects: pulse, eyes, voice, touch, colour, tongue, faeces, and urine.