Within different cultures herbal medicines have been used in different ways. In Britain, until relatively recent times, there were folk healers with a reputation for curing particular complaints. These people often learned their skill from their parents and would typically only use a small number of plants and would only claim to be able to help one or two types of affliction. The old herbals in this country were to some extent originally compilations of such information.

Traditional healers around the world have learned to find plants within their immediate environment that help to heal a range of illnesses and injuries. Virtually all tribal peoples around the world employ some form of herbal medicine. Many cultures have developed complex theoretical frameworks for understanding both disease and the application of herbs as medicine. Herbal medicines are an important part of Traditional Chinese medicine, of Ayurvedic practice in India, and of Tibb Unani medicine across the Islamic world. Herbs were the main tools for improving health in the ancient Greek theories of health and illness and these formed the basis of medical knowledge in Europe up until the modern era.

Over thousands of years of trial and error use, detailed pictures of the actions and applications of plant medicines have been compiled and refined. The theoretical constructs around their use change, but the plants remain. Over the last 150 years traditional descriptions of the ways in which plants work as medicines have been supplemented with biochemical analysis and research into plant pharmacology. Initially this research saw the development of pharmaceutical drugs derived from plant sources. Plants were analysed to determine which, of the dozens of complex organic compounds of which they are composed, were the "active constituents". The thinking was along the lines of "why give a patient a herb tea with an indeterminate amount of active ingredients, when it is possible to administer a small white pill with precisely measured amounts?" And so drugs such as digoxin, derived originally from foxgloves, and aspirin, based on chemicals found in meadowsweet and willow bark, were isolated and then synthesised artificially.

More recently we have discovered that the effect of isolating a medicinal compound from its parent plant usually increases the number of side effects associated with that drug. The substances in plants that chemists wanted to eliminate from medicines turn out to have a modulating effect on a herb's actions and are often beneficial. For example if meadowsweet is used as an anti-inflammatory, it does not have the stomach-irritating side effects that are associated with aspirin. It seems that nature has provided us with well formulated drugs in the form of the weeds that grow on our doorsteps!