1. Introduction
Traditional Thai medicine was strongly influenced by Ayurvedic medicine and Buddhism, which came from the Khmer and Mon people. In contrast to traditional Chinese medicine, it was mainly handed down orally from generation to generation without many written records of healing methods or recipes. Archeological evidence suggested the existence of healing pavilions, termed Arikhoya sala, in the Northeast of Thailand around the 12th century, when the Khmer dominated the region. Later on, the Thai migrated from Southern China to the region of contemporary Thailand and elements of traditional Chinese medicine were amalgamated with Thai medicine. A main principle of traditional Thai medicine is the four elements (Tart Chao Reun) that the human body consists of: earth, water, fire, and wind ( Thai Ministry of Public Health, 1986). A disequilibrium of one or more elements causes illnesses, and medicinal plants are used for correcting imbalances of the four elements. There is often a gradual transition between foods and herbal medicines, and controlling the diet represents an integral part of traditional Thai medicine. Modern handbooks on ancient Thai Materia Medica describe approximately 1500 items ( Mulholland, 1987).