Yao (Medicine) consists of neiyao, or jing, qi and shen, and waiyao, or medicine in real life. Both kinds of yao are important in qigong practice. Neiyao is all-effective, whilst waiyao is not so all the time; neiyao has no definite shape or form but exists in the body, whilst waiyao has its shape and form but does not really exist; neiyao can promote transcendence, whilst waiyao may help treat diseases; neiyao exists in your self, whilst waiyao comes from the human body; and neiyao clings to your body, whilst waiyao clings to the universe.
Neiyao can be produced all of a sudden but waiyao must be cultivated gradually over a long period of time. Neiyao is as important as waiyao, and you cannot do without waiyao. That is why you should cultivate neiyao whilst taking waiyao and train your mind whilst treating your body.
Chinese Qigong Illustrated
by Yu Gongbao