Clinical review

Herbal medicine

Andrew Vickers,  Catherine Zollman. 

	Background

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The use of plants for healing purposes predates human history and forms the origin of much modern medicine. Many conventional drugs originate from plant sources: a century ago, most of the few effective drugs were plant based. Examples include aspirin (from willow bark), digoxin (from foxglove), quinine (from cinchona bark), and morphine (from the opium poppy). The development of drugs from plants continues, with drug companies engaged in large scale pharmacological screening of herbs.

Until a century ago most effective medicines were plant based

Chinese herbalism is the most prevalent of the ancient herbal traditions currently practised in Britain. It is based on concepts of yin and yang and of Qi energy. Chinese herbs are ascribed qualities such as "cooling" (yin) or "stimulating" (yang) and used, often in combination, according to the deficiencies or excesses of these qualities in the patient.

Chinese herbalism is the most prevalent of the traditional herbal practices in Britain

Modern Western herbalism emphasises the effects of herbs on individual body systems. For example, herbs may be used for their supposed anti-inflammatory, haemostatic, expectorant, antispasmodic, or immunostimulatory properties.

Spending on herbal products in the United Kingdom is over £40m a year, mainly from self prescription of over the counter products. This type of herbal drug use is typically based on a simple matching of a particular herb to particular diseases or symptomssuch as valerian (Valeriana officinalis) for sleep disturbance. Originally confined to health food shops, herbal remedies are now marketed in many conventional pharmacies.

Differences from conventional drug use
Although superficially similar, herbal medicine and conventional pharmacotherapy have three important differences:

	What happens during a treatment?

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Herbal practitioners take extensive case histories and perform a physical examination. Patients are asked to describe their medical history and current symptoms. Particular attention is paid to the state of everyday processes such as appetite, digestion, urination, defecation, and sleep. Patients are then prescribed individualised combinations of herbs. These are usually taken as tinctures (alcoholic extracts) or teas. Syrups, pills, capsules, ointments, and compresses may also be used. Oral preparations can taste and smell unpleasant.

Herbal remedies are available in a wide variety of formulations

In addition to the herbal prescription, practitioners may work with their clients to improve diet and other lifestyle factors such as exercise and emotional issues. Follow up appointments occur after two to four weeks. Progress is reviewed and changes made to drugs, doses, or regimen as necessary.

	Therapeutic scope

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Although herbal preparations are widely used as self medication for acute conditions, practitioners of herbal medicine tend to concentrate on treating chronic conditions. A typical caseload might include asthma, eczema, premenstrual syndrome, rheumatoid arthritis, migraine, menopausal symptoms, chronic fatigue, and irritable bowel syndrome. Herbalists do not tend to treat acute mental or musculoskeletal disorders.

A substantial evidence base supports the use of St John's wort for treating mild to moderate depression

The aim of herbal treatment is usually to produce persisting improvements in wellbeing. Practitioners often talk in terms of trying to treat the "underlying cause" of disease and may prescribe herbs aimed at correcting patterns of dysfunction rather than targeting the presenting symptoms. That said, many practitioners prescribe symptomatically as well, such as giving a remedy to aid sleep in a patient with chronic pain.

Research evidence
In laboratory settings plant extracts have been shown to have a variety of pharmacological effects, including anti-inflammatory, vasodilatory, antimicrobial, anticonvulsant, sedative, and antipyretic effects. In a typical study an infusion of lemon grass leaves produced a dose dependent reduction of experimentally induced hyperalgesia in rat.

The dramatic responses of some patients' eczema after treatment by Dr Luo at the London Chinese Medical Centre prompted dermatologists to undertake randomised controlled trials of the herbal treatment

	Safety

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Many plants are highly toxic. Herbal medicine probably presents a greater risk of adverse effects and interactions than any other complementary therapy. There are case reports of serious adverse events after administration of herbal products. In most cases the herbs involved were self prescribed and bought over the counter or obtained from a source other than a registered practitioner. In the most notorious instance, several women developed rapidly progressive interstitial renal fibrosis after taking Chinese herbs prescribed by a slimming clinic.

Several herbal products interact with conventional drugssuch as echinacea (left) with anabolic steroids and valerian (right) with barbiturates

As well as their direct pharmacological effects, herbal products may be contaminated, adulterated, or misidentified. Adverse effects seem more common with herbs imported from outside Europe and north America. In general, patients taking herbal preparations regularly should receive careful follow up and have access to appropriate biochemical monitoring.

As with many complementary therapies, information on the prevalence of adverse effects is limited. The National Institute of Medical Herbalists and the University of Exeter have begun to operate a type of "yellow card" system to collect and collate adverse events reported by herbalists. The National Poisons Unit has set up a database to record adverse events and interactions, but, without a more systematic reporting scheme, the incidence of such events will remain unknown.

Interactions of herbal products with conventional drugs have been described. Some well characterised interactions exist, and competent medical herbalists are trained to take a detailed drug history and avoid these. Other interactions are not clearly defined. Problems are more likely to occur with less well qualified practitioners, more unusual combinations of agents, patients taking several conventional drugs, and those who self prescribe herbal medicines. If patients are taking conventional drugs, herbal preparations should be used with extreme caution and only on the advice of a herbalist familiar with the relevant conventional pharmacology.

	Practitioners

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Herbalists generally work as sole practitioners or in complementary medicine clinics. Few have conventional healthcare qualifications. There seems to have been little penetration of herbal medicine into the NHS. A small number of doctors practise herbalism, but this is often not integrated into their NHS work. Some ethnic groups have their own indigenous herbal practitioners, such as Hakims or Ayurvedic practitioners from the Indian subcontinent.

Many herbal prescriptions are individually formulated and dispensed by herbal practitioners themselves

Training
There are many different courses in herbalism and substantial variation in the content and standard of teaching. The most comprehensively trained practitioners are known as medical herbalists and are members of the National Institute of Medical Herbalists (NIMH). Their training usually includes at least 500 hours of supervised clinical practice and training in nutrition, communication skills, pharmacology, pharmacognosy, botany, pathology, conventional clinical diagnosis, biochemistry, physiology, and research skills. Courses last the equivalent of four years full time and lead to BSc degrees in herbal medicine.

Regulation
The National Institute of Medical Herbalists was set up in 1864 and remains the main registering and regulating body for Western herbal practitioners. Only graduates of approved courses are accepted on to the register, and a strict code of ethics is maintained.

	Footnotes

The ABC of complementary medicine is edited and written by Catherine Zollman and Andrew Vickers. Catherine Zollman is a general practitioner in Bristol, and Andrew Vickers will shortly take up a post at Memorial Sloan-Kettering Cancer Center, New York. At the time of writing, both worked for the Research Council for Complementary Medicine, London. The series will be published as a book in spring 2000.

The picture of a herbal dispensary is reproduced with permission of Paul Biddle/Science Photo Library. The pictures of Chinese herbal medicine are reproduced with permission of Rex Features/Hafenrichter. The picture of different herbal formulations is reproduced with permission of Alain Dex, Publiphoto Diffusion/Science Photo Library. The pictures of St John's wort and valerian are reproduced with permission of Glenis Moore/A-Z Botanical and A-Z Botanical. The picture of echinacea is reproduced with permission of NHPA/Stephen Krasemann. The picture of a Western herbalist is reproduced with permission of BMJ/Ulrike Preuss.