Using supplements with blood thinner may be risky, study finds

By Adi Narayan
Bloomberg News / May 15, 2010

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NEW YORK — People taking the blood thinner warfarin may have a higher risk of excessive bleeding or blood clots when using supplements containing gingko, garlic, and fish oil, a study found.

Many over-the-counter pills change the effectiveness of warfarin, marketed under the brand name Coumadin by Bristol-Myers Squibb, the research showed. Cranberry and glucosamine, for example, make the medication more potent, while ginseng and green tea extract make it too weak and ineffective at preventing clots in blood vessels.

Doctors consider warfarin difficult to manage because of side effects such as bleeding, and scientists have known that some popular health aids may cause adverse reactions when taken with prescription medicines.

Doctors should ask their patients about any supplements they may be taking before prescribing the blood thinner so that they can adjust the dose or take other precautions, according to the study.

“This is like a little wake-up call for me, to add an extra caveat that if you are going to take some herbal supplements, please let me know,’’ said Scott Monrad, an interventional cardiologist at the Montefiore Medical Center in New York, in a telephone interview.

The findings from the study by researchers from the University of Southern Nevada in Henderson, Nev., were presented Thursday at the annual meeting of the Heart Rhythm Society in Denver.

The research started with a survey finding 69 of 100 heart patients at Intermountain Medical Center in Salt Lake City took supplements and didn’t tell their doctors about it. Health supplements are sold over the counter in retail stores and aren’t regulated as drugs.

“Typically, people take supplements with the intention of improving their health; however, many supplements can have an undesirable interaction with other medications,’’ said Jennifer Strohecker, assistant professor of pharmacy practice at the University of Southern Nevada.

Strohecker and her colleagues reviewed data from case reports, randomized control studies, and animal experiments that focused on how supplements can change the way warfarin is absorbed in the body.

The medicine is prescribed to prevent blood clots that can lead to a heart attack or stroke.