Four Medical Codes is a Tibetan work that combines the essence of Tibetan medical theory and medical practice. Known in Tibetan. It was first compiled at the end of the 8th century by the Tibetan medical doctor Yutuo Ningmayuan Dangongbu (Lao Yutuo, 708-833), and later compiled by his descendant Yutuo Samayuan Dangongbu (Xiao Yutuo) in 1 1 century.