When 45-year-old Frances was diagnosed with bipolar disorder (manic depression), her doctor recommended lithium, a drug that must be precisely prescribed and closely monitored. After learning that lithium can interfere with kidney function, Frances started taking dandelion, an herb traditionally used to detoxify the kidneys. It didn’t occur to her to inform her doctor or pharmacist—not until after she had been rushed to the hospital and diagnosed with kidney failure. The dandelion’s diuretic properties had made the lithium more toxic. Ironically, the supplement she believed would protect her kidneys actually helped to destroy them.

Like Frances, 36% of U.S. adults use some form of complementary and alternative medicine (CAM), such as nutritional supplements, herbs and homeopathic remedies. Many don’t tell their doctor or pharmacist what CAM they’re taking. But whether it’s echinacea to fight colds or gingko biloba to improve memory, medicine by any other name is still medicine. The fact that it’s called “natural” or appeals to our sense of harmony with nature does not make it less potent. Taken alone or mixed knowingly or unknowingly with prescription or over-the-counter products, “holistic” remedies can cause adverse—even life-threatening—reactions. They can also alter your medical treatment and complicate surgical procedures. Telling your doctor you take them not only improves the probability that your health regimen will succeed, it can save your life.

For instance, Coumadin (a prescription drug that prevents blood clots), ginkgo, aspirin and vitamin E are all blood thinners. Combining any of them can up your risk of developing internal bleeding. St. John’s Wort can make certain HIV and cancer meds, birth control pills and prescriptions for heart disease, depression and seizures less effective.

Most doctors and druggists have not been trained in CAM, so you may be more knowledgeable than them. Yet they can still offer helpful advice on its safe and appropriate use based on their biomedical training and physiological knowledge. Also stay alert to health advisories about the products and the consequences of mixing them. You can keep up to date by searching the Index of Herbal Medicines and Supplements at www.Intelihealth.com.

Glenn Ellis is a homeopath and herbalist.