Shu Di Huang (Prepared Rehmannia glutinosa) is the premier yin tonic within Chinese medicine, older and more widely used than He Shou Wu. The kidney(s), according to Chinese medical thought, govern growth, reproduction, and development. They also house the Jing, or the constitutional allotment of every individial. Shu Di Huang is known as “The Kidney’s Own Food”. It is for the deepest level nourishment of (kidney)yin essence.