Do you know how many of your patients are taking herbal preparations? With the proliferation of herbal products, the number could be greater than you think. Between 1990 and 1997, the US population increased its use of herbal medicines by 380%.1 Total out-of-pocket expenditure for herbal medicines in 1997 was $5.1 billion.1Table 1 lists the 10 best-selling herbal medicines in the US.2
Safety issues related to herbal medicine are complex: possible toxicity of herbal constituents, presence of contaminants or adulterants, and potential interactions between herbs and prescription drugs. The quality of herbal medicines is often suboptimal. One reason for this is that they are not adequately regulated, and many experts are calling for a change in this situation. Cost-evaluations of herbal medicine are not available, so they cannot form the basis for clinical decisions.
This article provides guidelines for prescribing herbal medications appropriately.
TABLE 1
10 best-selling herbal medicines (United States, 2001)
| Rank | Herb | Retail sales |
|---|---|---|
| 1 | Ginkgo biloba | 46 |
| 2 | Echinacea | 40 |
| 3 | Garlic | 35 |
| 4 | Ginseng | 31 |
| 5 | Soy | 28 |
| 6 | Saw palmetto | 25 |
| 7 | St John’s wort | 24 |
| 8 | Valerian | 12 |
| 9 | Cranberry | 10 |
| 10 | Black cohosh | 10 |
| Retail sales are rounded figures in million US dollars. | ||
Efficacy
One of the first things to consider when a patient proposes trying an herbal medicine is efficacy. Data on efficacy of herbal medicines are incomplete, yet some treatments have shown promise. The critical question is, Does the remedy work for the patient’s condition? Clinicians should not prescribe or recommend herbal remedies if that question cannot be answered with a firm Yes.
Medical herbalism here and abroad
Medical herbalism (ie, the medicinal use of preparations that contain exclusively plant material) once dominated our pharmacopeia but went into rapid decline when pharmacology established itself as a leading branch of therapeutics. During the last part of the 19th and the early 20th century, herbalism virtually vanished from the therapeutic map of the US and the UK. In contrast, many developing countries never abandoned medical herbalism (Ayurvedic medicine in India, Kampo medicine in Japan, and Chinese herbalism in China). In other countries (such as Germany and France), medical herbalism continued a “low-key” coexistence with modern pharmacology. More recently, herbal medicine has experienced a remarkable comeback.
Herbal medicines usually contain a range of pharmacologically active compounds. In some cases it is not known which of these constituents produces the therapeutic effect. Testing for efficacy in this situation is obviously more complex than with synthetic drugs. One approach is to view the entire herbal extract as the active component. To optimise the reproducibility of efficacy studies, extracts must be sufficiently characterised. This is often achieved by standardizing the amount of a single key constituent of the extract (eg, a pharmacologically active ingredient or, if such an ingredient is not known, a marker suitable substance).
Other than the dilemma of standardization, herbal medicines can be scrutinized in clinical trials in much the same way as are other drugs. Several randomized clinical trials of herbal medicines have been published, and systematic reviews/meta-analyses of these studies have become available (Table 2).3,4 The Cochrane database includes about 30 systematic reviews of herbal medicines, and several authoritative books have recently become available.3-6 The conclusions of systematic reviews are often limited by the paucity and varied methodological quality of the primary studies.3,7 Research funds in this area are generally scarce, not least because plants are not patentable.
Generalizations about efficacy of herbal medicines are not possible; each one must be judged on its own merits. Some herbal products have demonstrated efficacy for certain conditions, while others have not. Most products have not been submitted to extensive clinical testing.3 “Clinicians should not prescribe or recommend herbal remedies without well-established efficacy….”7
TABLE 2
Examples of systematic reviews and meta-analyses of herbal remedies
| Common (Latin) name | Active ingredients | Indications | No. of trials | Avg. methodological quality of primary studies | Efficacy | Main result |
|---|---|---|---|---|---|---|
| Feverfew (Tanacetum parthenium) | Parthenolide | Migraine prevention | 5 | Good | Likely | 3 trials were positive, 2 were negative |
| Garlic (Allium sativum) | Alliin | Hypercholesterolemia | 13 | Good (some excellent) | Certain but effect small | Overall effect is significant but of debateable clinical relevance |
| Ginkgo (Ginkgo biloba) | Ginkgolides, bilobalide | Intermittent claudication | 8 | Good to excellent | Certain | Overall positive result |
| Horse chestnut seed extract (Aesculus hippocastanum) | Triterpene saponins | Chronic venous insufficiency | 8/5* | Good | Likely | Active treatment more effective than placebo and equally effective as reference treatments |
| Peppermint oil (Menta x piperial)† | Menthol | Symptoms of irritable bowel syndrome | 8 | Good | Likely | Positive effect of peppermint oil compared with placebo |
| Sources: Ernst et al 20013; Fugh-Berman 2003.4 | ||||||
| *8 trials vs placebo; 5 trials vs reference treatments. † Am J Gastroenterol 1997; 93:1131–1135. | ||||||
Safety
Consumers are attracted to herbal medicines in part because they equate “natural” with “safe.” Yet some herbal medicines pose serious risks.7
First, the active ingredients in herbal preparations can, of course, cause desirable as well as undesirable effects. Table 3 lists examples of commonly used herbal medicines that have been associated with serious adverse effects.3 Traditional use is no guarantee of safety and no acceptable substitute for data.8