Prescribing herbal medications appropriately
A poignant example is kava (Piper methysticum), an herbal remedy that has been used for centuries apparently without problems. Numerous rigorous clinical trials have shown it to be a powerful anxiolytic medicine.9 Recently it has been associated with several cases of serious liver damage.10 Hence it has been withdrawn from the markets of several European countries, and the FDA has issued warnings about its hepatotoxic potential.
Second, the active ingredients in herbal medicines might interact with prescription drugs. For instance, extracts of St. John’s wort (Hypericum perforatum) act as an enzyme inducer on the cytochrome P450 system and increase the activity of the P-glycoprotein transmembrane transporter mechanism. Both effects lead to a reduction of the plasma level of several conventional drugs.11 Perhaps the most serious consequence could be insufficiently low cyclosporine levels in patients after organ transplantation, which jeopardize the success of this procedure.12
Third, some herbal medicines (particularly Asian herbal mixtures) have repeatedly been shown to be contaminated with heavy metals,13 or to contain misidentified herbal ingredients that turned out to be toxic,14 or to be adulterated with prescription drugs.15
Before prescribing or recommending an herbal medication, clinicians must ensure that it cannot generate undue harm.
TABLE 3
Examples of herbal medicines associated with serious adverse effects
| Common (Latin) name | Indication | Adverse effects (examples) |
|---|---|---|
| Aloe vera (Aloe barbadensis) | Various | Juice may cause intestinal pain and electrolyte loss |
| Feverfew (Tanacetum parthenium) | Migraine prevention | “Post-fever syndrome” after discontinuation (migraine, anxiety, insomnia, muscle stiffness) |
| Hawthorn (Crataegus) | Congestive heart failure | Additive effects with other cardiac glycosides |
| Kava (Piper methysticum) | Anxiety | Toxic liver damage |
| St. John’s wort (Hypericum perforatum) | Depression | Increased clearance of a range of prescribeddrugs |
| Tea tree oil (Malaleuca alternifolia) | Skin problems (external) | Allergic reactions |
| Valerian (Valeriana officinalis) | Insomnia | Morning hangover |
| Without positive data demonstrating safety, herbal medications cannot automatically be considered safe for pregnant or nursing women. | ||
Quality
The quality of an herbal preparation partly determines its efficacy as well as its safety. Herbal dietary supplements are not usually regulated as drugs and have repeatedly been found to vary in quality, sometimes being suboptimal.7,16
In the US, such preparations have to meet the requirements set forth in the Dietary Supplement and Health Education Act (DSHEA) of 1994. Thus they are marketed without approval of their efficacy and safety by the FDA. The DSHEA does not allow medical claims to be made for such products. Structure or functional claims are, however, allowed. If safety concerns of a product arise, the burden of proof lies not with its manufacturer but with the FDA. Many experts find this regulation insufficient to guarantee consumer safety and argue for it to be changed.16 In Europe, new legislation will soon regulate herbal medicines. Essentially the legislation will provide that efficacy be demonstrated on the basis of bibliographic data; safety, too, will be governed as it is with conventional drugs.17
Cost
Clinicians should recommend treatments that save money for patients and the healthcare system. Many herbal medications are relatively inexpensive. However, very few proper economic analyses of herbal medicines exist.18,19 So far, only 1 cost evaluation of an herbal medicine has been published.20 This study of symptomatic treatment of chronic venous insufficiency compared the cost-effectiveness of compression stockings with that of an extract of horse chestnut seeds. Its results implied that the treatments were similarly effective and associated with similar costs.
For the prescribing physician, this means decisions cannot presently be based on conclusive cost-analyses. While waiting for such data to become available, decisions will have to be informed by our knowledge on the efficacy, safety, and quality of herbal medications.
Correspondence
Edzard Ernst, MD, PhD, Complementary Medicine, Peninsula Medical School, Universities of Exeter and Plymouth, 25 Victoria Park Road, Exeter EX2 4NT, United Kingdom. E-mail: Edzard.Ernst@pms.ac.uk.
