The Four Tantras are the fundamental text of the Tibetan medical tradition, claimed to have been taught by the Buddha himself. The first tantra or “root” tantra contains an overview of the medical system, while the second or “explanatory” gives more detail on theory and physiology. The third or “instructional” tantra gives information on treatments, while the fourth or “subsequent” tantra gives a variety of additional information on diagnosis, the preparation of medicines, and more.