A Warning on Medicinal Herbs 

Herbal remedies may be popular, but just how many of the hundreds of herbs on the market act on the body isn't clear. Although many studies on herbs have been done over the years, few have been well designed by Western standards. For instance, although St. John's wort is effective for mild to moderate depression, and doctors know the active ingredient, they aren't sure exactly how it works. 

Deciding how much of an herb to take can be a problem, says Wendy Warner, M.D., who specializes in women's health in Langhorne, Pa. Because herbs are not regulated, many times the dosage listed on the bottle isn't what you should take.

Taking too much of an herb could have toxic side effects, or taking it with a prescription or over-the-counter drug could cause unforeseen medical problems. St. John's wort, for example, has been clearly demonstrated to counteract anti-rejection drugs used in transplant patients. Taking this herb may result in rejection of the transplanted organ in as little as one to two days. In addition, St. John's wort may decrease the effectiveness of oral birth control pills.

Another problem with herbal studies is that the function of the active ingredient might have been misinterpreted. Studies on beta carotene, for example, found that it helped prevent cancer, based on consumption of whole vegetables and singling out beta carotene as the key ingredient in those vegetables. Further studies, however, found that giving just beta carotene to patients who smoked actually increased their risk for lung cancer. It turns out that beta carotene works in conjunction with other chemicals in the vegetables as a cancer fighter. Researchers concluded that it's better to eat a healthy diet including both fruits and vegetables than a supplement of beta carotene. This concept may well be applied to supplements with other single vitamins or minerals.