Before the Chinese invasion of 1959, medicine in Tibet was largely under the control of the lamas and closely linked with religion. Medical students memorized four complex "tantras," which explained the cause and progression of disease with the aid of "illustrated trees of medicine." Physicians used meditation and mantras to "energize" the medicine and increase its efficacy, and harvesting of herbs also carefully timed to use any helpful astrological influences.

Trees of medicine - Each leaf of the "illustrated tree" represented a cause of disease, a humor, or influence on outsome (the patient's age, his or her karma, the season of the disease, and so on).