The use of herbs to treat disease is almost universal among non-industrialized societies. A number of traditions came to dominate the practice of herbal medicine at the end of the twentieth century:
- The "classical" herbal medicine system, based on Greek and Roman sources
- The Siddha and Ayurvedic medicine systems from various South Asian Countries
- Chinese herbal medicine (Chinese herbology) (zhōngyào)
- Unani-Tibb medicine
- Shamanic herbalism: a catch-all phrase for information mostly supplied from South America and the Himalayas
Many of the pharmaceuticals currently available to physicians have a long history of use as herbal remedies, including opium, aspirin, digitalis, and quinine. The World Health Organization (WHO) estimates that 80 percent of the world's population presently uses herbal medicine for some aspect of primary health care. In comparison, herbal medicines can be grown from seed or gathered from nature for little or no cost. Herbal medicine is a major component in all traditional medicine systems, and a common element in Siddha, Ayurvedic, homeopathic, naturopathic, traditional Chinese medicine, and Native American medicine. Pharmaceuticals are prohibitively expensive for most of the world's population, half of which lives on less than $2 U.S. per day.
