Over a person's lifetime they are likely to be prescribed more than 14,000 pills. Antibiotics, cholesterol lowering tablets, anti-depressants, painkillers, even tablets to extend youth and improve performance in bed. These drugs perform minor miracles day after day, but how much is really known about them? Drug discovery often owes as much to serendipity as to science, and that means much is learnt about how medicines work, or even what they do, when they're taken. By investigating some of the most popular pills people pop, Horizon asks, how much can they be trusted to do what they are supposed to?

The documentary 'The Knowledge of Healing' is an illuminating examination of Tibetan medicine, a practice which has developed over two millennia into a modern day successful method of healing that rivals western medical practices. Unlike Western medicine, based on biochemistry, Tibetan medical thinking (which is strongly rooted in Buddhist principles) views the human body as governed by an elaborately organized system of energies flowing through a network of channels. In the 12th century, the Gyüshi (Knowledge of Healing) was created, a text codifying this intricate system. The medications used comprise herbs, roots, minerals, etc. After flourishing for centuries, most Tibetan medical schools were destroyed by the Chinese in the 1950's and 1960's, and many physicians were executed. Speaking from exile, the Dalai Lama argues for the value of Tibetan medicine, while his personal physician Dr. Tenzin Choedrak describes the principles behind it. We follow physicians in India and Siberia treating patients for a variety of ailments from paralysis to heart disease, and meet researchers in Israel and Switzerland to see how western clinical studies are testing the effectiveness of Tibetan medicine.