Herbal Remedies: Adverse Effects and Drug Interactions

A growing number of Americans are using herbal products for preventive and therapeutic purposes. The manufacturers of these products are not required to submit proof of safety and efficacy to the U.S. Food and Drug Administration before marketing. For this reason, the adverse effects and drug interactions associated with herbal remedies are largely unknown. Ginkgo biloba extract, advertised as improving cognitive functioning, has been reported to cause spontaneous bleeding, and it may interact with anticoagulants and antiplatelet agents. St. John's wort, promoted as a treatment for depression, may have monoamine oxidase­inhibiting effects or may cause increased levels of serotonin, dopamine and norepinephrine. Although St. John's wort probably does not interact with foods that contain tyramine, it should not be used with prescription antidepressants. Ephedrine-containing herbal products have been associated with adverse cardiovascular events, seizures and even death. Ginseng, widely used for its purported physical and mental effects, is generally well tolerated, but it has been implicated as a cause of decreased response to warfarin. Physicians must be alert for adverse effects and drug interactions associated with herbal remedies, and they should ask all patients about the use of these products.

Increasingly, alternative therapies such as herbal products are being used in the United States. Approximately 25 percent of Americans who consult their physician about a serious health problem are employing unconventional therapy, but only 70 percent of these patients inform their physician of such use.

Herbal products are not tested with the scientific rigor required of conventional drugs, and they are not subject to the approval process of the U.S. Food and Drug Administration (FDA). Herbal products therefore cannot be marketed for the diagnosis, treatment, cure or prevention of disease. Nonetheless, the Dietary Supplement Health and Education Act of 1994 allows these products to be labeled with statements explaining their purported effect on the structure or function of the human body (e.g., alleviation of fatigue) or their role in promoting general well-being (e.g., enhancement of mood or mentation).² Analysis of some of the putative effects of herbal products shows that they sometimes closely resemble claims of clinical efficacy for various diseases or conditions.

Unlike conventional drugs, herbal products are not regulated for purity and potency.² Thus, some of the adverse effects and drug interactions reported for herbal products could be caused by impurities (e.g., allergens, pollen and spores) or batch-to-batch variability. In addition, the potency of an herbal product may increase the possibility of adverse effects.

Because physicians are likely to encounter patients who are using herbal remedies, they need to be aware of the purported effects of these products. They also need to be cognizant of the adverse effects of herbal remedies and the possibility of deleterious drug interactions.