Herbs have been used for medicinal purposes for centuries, and numerous drugs we have today originated from plants - for example aspirin, digoxin, quinine, and morphine. Such developments from plants to medicines continue today, with most research-based pharmaceutical companies screening plant derivatives for active substances. There is often a blurring of distinction between conventional and so-called complementary medicines, and this is the case with herbal medicines. If someone is seriously ill and their illness responds to an herbal medicine, they don't feel its important to distinguish between 'conventional' and 'complementary' medicines; they are just delighted to have an effective medicine.

The British Medical Journal is publishing a series of articles on complementary medicine, and "Herbal Medicine" is a recent piece in that series. The use of medicinal herbs has increased considerably in recent years in all developed countries, largely because of perceived dissatisfaction with the cost/benefits provided by traditional medicines. Herbal drugs are often cheaper and more readily obtained than conventional drugs, and the claims regarding their efficacy are not usually under regulatory control, so that exaggerated promises are often made. While both self-medication with herbs and the practice of herbal medicine are enjoying this increased popularity, the article summarized here is chiefly concerned with the practice of herbal medicine.

Herbalists generally work as solo practitioners, or in complementary medicine clinics. Only a few possess conventional health-care professional qualifications. Some have had comprehensive training in herbal medicine lasting up to two years, while others have merely completed a two-day introductory course leading to a diploma. Some countries have set up institutions or certification programs, which may one day leads to registers of qualified herbal practitioners. However, the ethnic differences in the types of herbal medicine (Chinese, Ayurvedic, etc) work against this sort of certification.

The practice of herbal medicine differs in several important ways from that of conventional medicine. First, the whole plant is used in herbal preparations, usually as an unpurified extract containing several different constituents. Herbalists claim that the constituents can work together synergistically, whereas toxicity is reduced because of a "buffering" effect of one constituent by another. Often several different herbs are used together, a procedure which is claimed to enhance these principles of synergy and buffering.

An herbal practitioner takes a history and performs a physical exam in the same way as a medical practitioner, although the emphasis is on every day processes such as appetite, digestion, excretion and sleep. The rationale for prescribing an herbal medication is not usually expressed as a medical indication, but rather as a fault detected in one of a patient's normal bodily function. For instance, an herbal practitioner will speak of "the underfunctioning of the systems of elimination" in arthritis, and prescribe a diuretic or laxative combination of herbs, together with some having intrinsic anti-inflammatory properties. Different combinations of herbs are prescribed on an individual basis, accompanied by advice on necessary diet and lifestyle changes.
Plant extracts contain numerous pharmacologically active substances, and appropriate extracts will exert recognizable pharmacodynamic effects, if given in appropriate doses. Several individual herbs have been shown in well-controlled clinical studies to be efficacious and safe: St. John's wort, ginger, feverfew, and gingko are among them.
However, the authors of the review go on to state that there is "very little evidence on the effectiveness of herbalism as practiced - that is, using principles such as combining herbs and unconventional diagnoses". One of the few randomized studies reported examined the use of a traditional Chinese herbal eczema treatment in 87 adults and children refractory to conventional therapy. They participated in a crossover study comparing a preparation of 10 Chinese herbs with a placebo containing herbs regarded as ineffective in eczema. There were highly significant reductions in eczema scores with the active preparation, and long-term follow-up showed that benefits were maintained with continued treatment¹.

Toxicity can be a problem with herbal medicines. Some well-known herbs have intrinsic toxic effects - a well-publicized incident involved the occurrence of interstitial renal fibrosis following Chinese herbs prescribed for weight loss. More important than intrinsic toxicity, however, the risk of contamination, adulteration or false identity can have serious consequences. Herbal preparations are not generally regulated for safety and content uniformity in the same way as conventional medicines.

Pharmacokinetic interactions can occur between herbs and conventional drugs. Perhaps the best-known example is the effect of St. John's wort on the blood levels of numerous conventional drugs; the types of drugs affected include oral contraceptives, some antihypertensives, anticonvulsants, cyclosporine, and some antibiotics and antifungal medicines. The article contains a table listing 22 herbs that may have important potential interactions with conventional drugs. It is therefore important for physicians and pharmacists, before prescribing a drug, to enquire not only about conventional drugs, but also about herbs and supplements that the patient may already be taking.

This review article provides an objective digest of the role of herbal medicine in the overall medical treatment landscape. The authors have recently published their "ABC of Complementary Medicine", which covers, in addition to herbal medicine, other aspects of non-conventional medical treatment, such as acupuncture, nutritional supplements, and massage therapy.