Mixing medications with dietary supplements, such as vitamins and herbal products, can be dangerous, the U.S. Food and Drug Administration (FDA) has cautioned.

Certain dietary supplements can boost the effects of other medications as well as change how the human body processes medications, according to the FDA, thereby changing the blood levels of that medication.

“[Patients] may be getting either too much or too little of a medication [they] need,” FDA Medical Officer Robert Mozersky says in a recent FDA news release.

“Some dietary supplements may increase the effect of your medication, and other dietary supplements may decrease it.”

For example, birth control pills and drugs designed to treat HIV/AIDS, heart disease and depression are less effective when taken with St. John’s wort, an herbal supplement, according to the FDA. Reduced or increased efficacy of certain medications could result in potentially harmful adverse drug events or treatment failures.

A 2008 review study in the journal American Family Physician lists St. John’s wort as the supplement with the most documented interactions with drugs. The paper by Gardiner et al. advises physicians to ask what dietary supplements their patients are taking and document this information in their patient record.

FDA officials also warn against combining supplements that thin the blood, such as ginkgo biloba and vitamin E, with warfarin, a common medication prescribed for cardiovascular disease or blood clots. Taking any of these products together may increase the risk for internal bleeding or stroke, the FDA warns.

Use of supplements in the U.S. appears to be on the rise. According to the Centers for Disease Control and Prevention (CDC), more than 40 percent of the U.S population used supplements between 1988 and 1994, while more than one-half used them between 2003 and 2006. Multivitamins and multiminerals are the most commonly used dietary supplements, the CDC reports, with approximately 40 percent of men and women reporting use between 2003 and 2006.

The YouScript Personalized Prescribing software database contains hundreds of dietary supplements currently on the market and can detect potential interactions with hundreds of other medications, both prescription and over the counter. Unique among drug interaction software, YouScript can detect interactions between three or more medications and then offer alternatives with a lower risk of interactions.

Find more information on dietary supplements on the FDA’s website.