Background

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.

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 qualifies in the patient.

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 [pounds sterling] 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 symptoms--such 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:

Use of whole plants--Herbalists generally use unpurified plant extracts containing several different constituents. They claim that these can work together synergistically so that the effect of the whole herb is greater than the summed effects of its components. They also claim that toxicity is reduced when whole herbs are used instead of isolated active ingredients ("buffering"). Although two samples of a particular herbal drug may contain constituent compounds in different proportions, practitioners claim that this does not generally cause clinical problems. There is some experimental evidence for synergy and buffering in certain whole plant preparations, but how far this is generalisable to all herbal products is not known.

Herb combining--Often, several different herbs are used together. Practitioners say that the principles of synergy and buffering apply to combinations of plants and claim that combining herbs improves efficacy and reduces adverse effects. This contrasts with conventional practice, where polypharmacy is generally avoided whenever possible.

Diagnosis--Herbal practitioners use different diagnostic principles from conventional practitioners. For example, when treating arthritis, they might observe "underfunctioning of a patient's systems of elimination" and decide that the arthritis results from "an accumulation of metabolic waste products." A diuretic, choleretic, or laxative combination of herbs might then be prescribed alongside herbs with anti-inflammatory properties.

What happens during a treatment?

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.

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

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.

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.

Human studies also confirm specific therapeutic effects of particular herbs: randomised controlled trials support the use of ginger for treating nausea and vomiting, feverfew for migraine prophylaxis, and ginkgo for cerebral insufficiency and dementia. The best known evidence about a herbal product concerns St John's wort (Hypericum perforatum) for treating mild to moderate depression. A systematic review of 23 randomised controlled trials found the herb to be significantly superior to placebo and therapeutically equivalent to, but with fewer side effects than, antidepressants such as amitriptyline.

However, there is still very little evidence on the effectiveness of herbalism as practised--that is, using principles such as combining herbs and unconventional diagnosis. Almost no randomised studies have investigated herbal practitioners treating as they would in everyday clinical work. Perhaps the closest attempt evaluated a traditional Chinese herbal treatment of eczema. As prescriptions depend on patients' exact presentations, only those with widespread, non-exudative eczema were included. Eighty seven adults and children, refractory to conventional first and second line treatment, were randomised to a crossover study that compared a preparation of about 10 Chinese herbs with a placebo consisting of herbs thought to be ineffective for eczema. Highly significant reductions in eczema scores were associated with active treatment but not with placebo. At long term follow up, over half of the adults (12/21) and over 75% of the children (18/23) who continued treatment had a greater than 90% reduction in eczema scores.

Safety

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.

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.