As with other alternative therapies, the Brits are turning to herbal remedies in droves. We now spend pounds 300m a year on over-the-counter herbal health supplements, among them valerian (to promote sleep), garlic (to lower cholesterol) and arnica (to relieve bruising). And last week, the first herbal medicine clinic to be established in an NHS hospital opened in London. The charity-funded Archway Clinic, based at the Whittington Hospital, is already fully booked for the next month.

Do herbal remedies work? In the eyes of many doctors, they certainly have more credibility than other alternative treatments, not least because so many successful drugs derive from them. Digoxin, used to treat heart disease, originated from foxgloves; morphine, a powerful analgesic, came from the opium poppy. Ephedrine, a decongestant and bronchodilator, is a constituent of the Chinese herb ma huang, while taxol, used in the treatment of breast and ovarian cancer, is derived from the needles and twigs of the European yew.

But isolating the active ingredient in a plant and producing a synthetic version in the lab is a far cry from the approach of the traditional herbalist, who would argue that the whole plant - sometimes several plants - has to be used in a remedy to protect against harmful side effects. The active ingredient of willowbark, for instance, is salicylic acid - the herbal equivalent of aspirin. Willowbark acts in the same way as aspirin but because it contains other substances which are natural protectors of the stomach lining it does not irritate the stomach (which may be crucial if you have a sensitive stomach and suffer from chronic arthritis but not so vital if you simply want to zap a raging headache).

Like other alternative practitioners, herbalists tend to take the holistic approach - definitely part of the attraction, if you see nothing more of your GP than the time it takes to write a prescription - and believe that their job is to promote the body's capacity for self-healing. For a fee which can range from pounds 20 to pounds 50, they normally spend the best part of an hour discussing factors such as lifestyle, diet and relationships before making up the remedy: in European herbalism, this normally comes in the form of a tincture, in which the herbs are steeped in alcohol for two weeks and the liquid then strained. Although herbs bought over the counter are sold as food supplements, herbalists are allowed to prescribe under the1968 Medicines Act.

There seems little doubt that some of these remedies are effective. In Germany, where herbal treatments are more part of mainstream medicine, rigorous scientific trials have found St John's Wort, or hypericum, to be effective as an anti-depressant - without the side effects of orthodox drugs - while gingko biloba (the latest wonder herb) has been found to improve blood flow to the nervous system and is taken to help prevent strokes and dementia. Even in Britain where attitudes are more sceptical, evening primrose oil now has a medical licence for the treatment of breast pain, and trials of Chinese herbal medicine have found it effective for the treatment of eczema in children.

Herbal medicine will probably best suit those who have chronic ailments such asmigraine, arthritis, skin disorders and digestive problems. But although they are promoted as more gentle than orthodox drugs, some herbs can have toxic side effects: comfrey, used to treat gastric ulcers, has been linked to liver damage. There is particular concern about Chinese herbal medicine: the lack of quality control over imports and "cowboy" practitioners are resulting in harmful, sometimes lethal side effects. Herbs should not be used in conjunction with orthodox drugs unless a qualified herbalist or GP is consulted; pregnant women should take particular care.

For a list of qualified practitioners, telephone the National Institute of Medical Herbalists, on 01392 426022, or the Register of Chinese Herbal medicine, 0181 834 6229. For coughs and colds, try grated fresh ginger, which encourages sweating; and for cuts and grazes, calendula or marigold cream, both natural antisepticsn