Warning for users of warfarin

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SALT LAKE CITY -- There is a warning Monday to users of the prescription drug known as warfarin. If you're using the medication, which is designed to prevent blood clots, beware of mixing it with herbal and dietary supplements. Twenty seven of the top 40 selling supplements have a dangerous interaction. Out of the top 10, nine interact with the blood thinning medication.

Warfarin brand names
  • Coumadin
  • Jantoven
  • Marevan
  • Lawarin
  • Waran

Jennifer Strohecker, a Pharm D researcher at Intermountain Medical Centers Heart Institute said, "Glucosamine/chondroitin, fish oil, melatonin, coenzyme Q10 and multivitamins containing vitamin K have the potential to interact with warfarin."

Warfarin and herbal and dietary supplements "compete" in the liver. This competition changes the way the blood thinner works, thereby increasing the risk of bleeding, or by reducing its effectiveness, increasing the risk of stroke, said Dr. T. Jared Bunch, a heart rhythm specialist at the heart institute.

"This data is important because it demonstrates how important it is for physicians to understand our patients' knowledge about and use of these products," Bunch said. "We need to do a better job of teaching our patients about the dangers of mixing warfarin with these products."

What is... warfarin?
Warfarin is a prescription drug used to prevent blood clots from forming or growing larger in your blood and blood vessels. It is prescribed for people with certain types of irregular heartbeat, people with prosthetic (replacement or mechanical) heart valves, and people who have suffered a heart attack. Warfarin is also used to treat or prevent venous thrombosis (swelling and blood clot in a vein) and pulmonary embolism (a blood clot in the lung).

Heart patient Marc Buckley ate tons of spinach and broccoli, and took daily vitamin supplements. He still does, but now working with his physician, he's learned how to lower and balance what he's taking so as not to interfere with warfarin.

"Whereas before I might have spinach three meals in a row," Buckley says, "now it's more regular and consistent so that my levels stay in range." He's doing the same with vitamins.

Strohecker says, "Almost 90 percent of the patients we surveyed said that they would be comfortable speaking with their doctor or pharmacist about supplements, if they were asked." But doctors need to ask as well. The study says communication on both sides is absolutely essential for patient safety.


For 50 years, warfarin or coumadin has been the standard of care. It works very well as an anticoagulant, but it's super-sensitive to interactions. That's why the FDA has approved and added a new drug to the arsenal that may not have the same problems. Unlike warfarin, the new drug called dabigatran does not require continual blood tests, nor does it appear to have all the drug-drug, drug-supplement or drug-food interactions.

In the U.S. alone, pharmacists fill 2.2 million prescriptions for warfarin every year.

E-mail: eyeates@ksl.com

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