Nearly half of Americans take at least one prescription drug, and one in six takes three or more, according to a new report from the U.S. Department of Health and Human Services. Plus, recent surveys reveal that a growing number of individuals also take over-the-counter (OTC) medications and herbal products. The result? Potential for unintended side effects or interactions that change the way the medications work. Here are some examples:

• Decongestants: Commonly found in OTC cold and allergy medications, decongestants can increase blood pressure in people who take medicine to lower their blood pressure. Decongestants also can cause blood pressure to rise in those who are taking antidepressants called MAO inhibitors.
• St. John’s wort: This popular herb is used to combat depression. But St. John’s wort can interact harmfully with many different OTC and prescription medicines. These include tranquilizers, sleeping pills, antidepressants, the asthma drug theophylline, and popular cholesterol-lowering drugs called statins. It can be harmful if taken with alcohol, too.
• Blood thinners: Drugs such as warfarin help prevent blood clots in people prone to stroke and heart attack. Combining prescription blood thinners with aspirin, acetaminophen, or naproxen could cause excessive bleeding.

Many herbal supplements also interact with warfarin. One new study in the Annals of Internal Medicine reports that ginseng can hamper warfarin’s blood-thinning effect. Other herbs, such as dong quai and ginkgo biloba, may increase bleeding if taken at the same time as warfarin.

Did You Know?
You should avoid grapefruit juice if you’re taking certain blood pressure drugs called calcium-channel blockers or statin-type cholesterol-lowering drugs.