Herbal remedies may be popular, but just how many of the hundreds of herbs on the market act on the body isn't clear. Many herbal remedies come from folk medicine. Although many studies on herbs have been done over the years, few have been well designed by Western standards. For instance, although Saint-John's-wort is effective for mild to moderate depression, and doctors know the active ingredient, they aren't sure exactly how it works. Remedies such as chamomile, ginger, and kava have been used for centuries but only now are beginning to be scientifically investigated.
Deciding how much of an herb to take can be a problem because herbs are not regulated; often the recommended 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. Saint-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, Saint-John's-wort may decrease the effectiveness of oral birth control pills. Although many people think that herbs cannot harm, many herbal medicines have side effects like medicines. Saint-John's-wort, for example, can interact with sunlight to cause skin irritation and sunburn.
Another difficulty in studying herbal remedies is what scientists think is the active ingredient, may not be. Herbs contain multiple potentially active ingredients. 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 produces its effect in combination 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.