Patients who self-medicate with herbs for preventive and therapeutic purposes may assume that these products are safe because they are "natural," but some products cause adverse effects or have the potential to interact with prescription medications.

The United States lacks a regulatory system for herbal products. Although only limited research on herbs has been published, St John's wort shows promise as a treatment for depression. Ginkgo biloba extract is possibly effective for cerebrovascular insufficiency and dementia.

Feverfew is used extensively in Canada for migraine prophylaxis but needs more rigorous study. Ephedrine has been regulated by many states because its misuse has been associated with several deaths.

Echinacea is being tried as an agent for immune stimulation, and garlic is under study for cholesterol-lowering properties, but both require more study. Physicians should educate themselves and their patients about the efficacy and adverse interactions of herbal agents and the limitations of our present knowledge of them.A significant minority of American adults self-medicate with herbal preparations for preventive or therapeutic purposes.

Sales of herbal products in the United States have increased sharply in recent years, according to industry reports. An estimated $2 billion was spent in health food stores in 1996 for herbs in bulk, as well as capsules, tablets, extracts and teas.1 A 1995 telephone survey of 136 customers who purchased supplements at two health food stores in Milwaukee during a 15-day period found that the respondents were taking a total of 805 supplements, an average of 5.9 supplements per person. Of this group, 85 percent reportedly had a regular physician.2