There is an unspoken "don't ask, don't tell" at work in most doctors' offices. Physicians don't ask and patients rarely tell about herbs and dietary supplements.

Many people worry that their doctors will disapprove of products such as ginseng or ginkgo, so they don't mention what they are taking. But their silence could be deadly.

Researchers are gradually uncovering dangerous interactions between herbs and medications. With millions of people taking herbs to improve memory, enhance energy and relieve depression or hot flashes, there is a tremendous potential for problems.

In the Jan. 8 issue of the Lancet, Dr. Adriane Fugh-Berman discusses interactions reported in medical literature. As she points out, "Concurrent use of herbs may mimic, magnify or oppose the effect of drugs."

St. John's wort, for example, is taken by millions of people to treat winter blues, insomnia, mild depression, PMS and other problems. But people who take this herb along with a prescription antidepressant such as Desyrel, Paxil, Serzone or Zoloft may experience something called "serotonin syndrome." Possible symptoms include tremor, nausea, digestive tract upset, restlessness, headache, muscle pain and confusion. Asthma drugs containing theophylline and oral contraceptives could also be less effective when taken with this herb.

People on the anticoagulant Coumadin (warfarin) are frequently cautioned about its potential for interacting with certain foods or other medicines. But they are rarely told that many herbs can adversely impact its action. Astragalus, dong quai, feverfew, garlic, ginkgo, ginseng, goldenseal, papaya and pau d'arco could be incompatible with Coumadin.

Licorice is a common ingredient in herbal teas and medicines. It is also a popular candy, but people should be cautious about combining licorice with medicines such as prednisone or hydrocortisone. Lanoxin and Lasix could be lethal if licorice depletes potassium from the body.

Even more alarming is the Chinese medicine ma huang (ephedra). This ingredient is cropping up in energy pills and herbal diet formulations. When taken with certain migraine medicines or antidepressants, blood pressure can go sky-high and lead to a stroke.

It's time to end the silence surrounding herbal supplements. Physicians should inquire about their use. Patients should volunteer information on what alternative treatments they are trying. Together they may be able to prevent dangerous interactions.