FDA Warns of Mixing Supplements with Prescriptions and OTCs

The FDA warned of dangerous outcomes when taking vitamins or other dietary supplements along with prescription or over-the-counter medications. Dietary supplements can alter the absorption and metabolism of these drugs, the FDA said.

"Some dietary supplements may increase the effect of your medication, and other dietary supplements may decrease it," said Robert Mozersky, medical officer, FDA, in a news release.

Examples include the supplement St. John's Wort can make birth control pills less effective; and both the herbal supplement ginkgo biloba and vitamin E can lead to blood thinning, as mixing either supplement with the prescription blood thinner warfarin or aspirin could increase the risk of internal bleeding or stroke.

The Centers for Disease Control and Prevention reports that nearly 72 million people in the United States who are on a prescription medication also take some type of dietary supplement, per their 2005 to 2008 National Health and Nutrition Examination Survey.

Although many people take supplements to make sure they get proper nutrition, the FDA said there is no substitute for eating a healthy diet, and products labeled as "natural" or "herbal" are not necessarily harmless. "Natural does not always mean safe," said Mr. Mozersky.

People planning to have surgery should inform their doctor of every medication and supplement they use. It may be necessary to stop taking supplements a few weeks before an operation to avoid potentially serious changes in heart rate, blood pressure, or bleeding risk, the FDA said.—Kerri Fitzgerald