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► anxiolytic medicine in rigorous clinical trials (Barnes et al. 1998). Recently, it has been associated with several cases of serious liver damage. Hence, it has been withdrawn from the markets of several European countries.

Second, the active principles in herbal medicines might interact with prescription drugs. A classic example of this scenario is provided by St. John's wort (Hypericum perforatum). One or several constituents of St. John's wort (most likely hypericin) act as an enzyme inducer on the

► cytochrome P450 system and increase the activity of the P-glycoprotein transmembrane transporter mechanism. Both mechanisms lead to a reduction of the plasma level of several conventional drugs (De Smet PAGM 2002). This can lead to a range of serious adverse effects.

Third, some herbal medicines (particularly Asian herbal mixtures) have been demonstrated repeatedly to be contaminated with heavy metals or adulterated, e.g., with prescription drugs. Because, in many countries (e.g., the USA and UK), most herbal medicines continue to be marketed as dietary supplements, their quality is not adequately controlled and suboptimal quality may put consumers at risk.

Finally, substitutions of one (innocent) herb from a herbal mixture with a toxic herb may occur either inadvertently or fraudulently. A famous example of such a scenario was the introduction of Aristolochia into a Chinese herbal mixture used for body weight reduction. This caused serious kidney damage and subsequent malignancies in many Belgian consumers (Ernst 2002).

Because positive safety data are usually not available, herbal remedies should be viewed as contra-indicated during pregnancy and lactation (Barnes et al. 1998). Our present post-marketing surveillance systems are likely to register only a minute proportion of all the adverse effects of herbal medicines. Consumers are less prone to report adverse effects of herbal medicines than those of other OTC medications (Ernst et al. 2006). As herbal medicines become more and more popular, we should find better ways of minimizing the risks that maybe associated with them.

Quality

Commercially available herbal products have repeatedly been found to be of varying and at times suboptimal quality (Guo et al. 2007). As pointed out earlier, poor quality can cause harm, for instance, in the case of contamination with toxic substances. Any clinical trial of insufficient herbal product would generate a negative result, even if the herb tested is per se efficacious.

In most countries, herbal medicines are marketed as dietary supplements with no need to demonstrate efficacy, safety, or quality in the way of licensed medicines. Thus, many products available to patients may be of inadequate quality, for example, they may be underdosed. For consumers, it is notoriously difficult to identify products of high quality. Table 3 lists some manufacturers known for their experience, quality, and investment into research.

Cost

Very few economic analyses of complementary/alternative medicines exist. The few that have been published are methodologically weak and, therefore, far from convincing.

Herbal Remedies. Table 3. Examples of manufacturers who market high-quality standardized products and invest in research.

Interestingly, retrospective analyses tend to suggest that complementary/alternative medicine can reduce costs, whereas (the more rigorous) prospective analyses tend to imply that the use of complementary/alternative medicine is associated with an increase in cost (Nortier and Muniz Martinez 2000). The situation with herbal medicines is much the same as with other complementary/alternative medicines.

Comment

Investigations of the efficacy, safety, quality, and cost of herbal medicines are feasible and, vis-a-vis, the popularity of such preparations is highly desirable. For some, but by no means all herbal medicines, efficacy data are now emerging (Barnes et al. 1998). They show that some herbal medicines are efficacious for certain indications. All herbal medicines are associated with safety issues which, in some instances, can be complex. Economic evaluations of herbal medicines are still extremely scarce.

Research into herbal medicines is much less active than research into conventional drugs. Lack of commercial impetus, owing to lack of patent protection, is one obvious reason. The legal status of herbal medicines might be another: as for dietary supplements, there is no formal obligation to prove efficacy. If we want to find the answers for many open questions in herbal medicine, we should consider other means of finding adequate funds for research in this area.

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