Medicinal plants

Medicinal plants have been identified and used throughout human history. Plants make many chemical compounds for biological functions, including defence against insects, fungi and herbivorous mammals. At least 12,000 such compounds have been isolated; this is estimated to be less than 10% of the total. These chemicals work on the human body in exactly the same way as pharmaceutical drugs, so herbal medicines can be beneficial and have harmful side effects just like conventional drugs. Further, plants may contain many different substances, so plant extracts may have multiple side effects.

The use of plants as medicines pre-dates written history. The earliest records of herbs are found from the Sumerian civilisation, where hundreds of medicinal plants including opium are listed on clay tablets. The Ebers Papyrus from ancient Egypt describes over 850 plant medicines. Ethnobotany, the study of traditional human uses of plants, is recognized as an effective way to discover future medicines. In 2001, researchers identified 122 compounds used in modern medicine derived from traditional plant sources; 80% of these have had a traditional use identical or related to the current use of the active elements of the plant. These include the common drugs aspirin, digoxin, quinine, and opium. The compounds found in plants are of many kinds, but most are in four major biochemical classes, the alkaloids, polyphenols, glycosides, and terpenes.

Herbs are widely used to treat disease in non-industrialized societies, not least because they are far cheaper than modern medicines. The annual global export value of pharmaceutical plants in 2012 was over US$2.2 billion.

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