Prescribing herbal medications appropriately

Journal of Family Practice, Dec, 2004 by Edzard Ernst

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. (1) Table 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.

* 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.

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)

* 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)

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.

* 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)