Americans are taking more prescription drugs than ever—along with more supplements. So it’s natural that questions about drug-nutrient interactions are also on the rise. Nearly half of Americans of all ages, and nine out of ten older Americans, now take at least one prescription drug, according to the Centers for Disease Control and Prevention (CDC). And more than half of American adults now take at least one dietary supplement, with multivitamins being the most common, according to a new CDC-sponsored study.

“Drugs are powerful substances that tend to work by blocking one pathway in the body,” says Robert Rountree, MD, Delicious Living’s medical editor and coauthor of the Clinical Natural Medicine Handbook (Mary Ann Liebert, 2008). “There’s a significant chance of an unexpected side effect. Often, you need to take a dietary supplement to replace depleted nutrients or protect against organ damage.”

Some nutrients can even enhance drugs’ effectiveness, says Leo Galland, MD, director of the Foundation for Integrated Medicine and founder of pilladvised.com. “But doctors are apprehensive about combinations of supplements and drugs because of mostly anecdotal reports of negative interactions. The supplement becomes the presumed culprit.”