Bleeding DisordersConsumer AlertHerbals

Risk of interactions between supplements and blood thinners

Dr. Jennifer Strohecker at the Intermountain Medical Center, in Salt Lake City, Utah, tells us the safety of warfarin (Coumadin) use can be compromised by many popular herbal and nonherbal supplements.

Here’s what we know from her research.

  • Of the 40 most commonly used herbal and nonherbal supplements, more than 50% have a direct or indirect interaction with warfarin.
  • Among the 10 most popular supplements, 80% are known to interact with warfarin.
  • Of the 40 herbal and nonherbals, 35% can significantly change the INR (test of clotting ability).
  • 9 supplements are known to increase the risk of bleeding.
  • 5 are known to decrease the effectiveness of warfarin.
  • Glucosamine, essential fatty acids, multiherb products, and primrose oil can increase prothrombin times, while coenzyme Q10, soy, melatonin, ginseng, and St John’s wort can decrease prothrombin times.

The bottom line?

Among users, belief in supplements often runs deep, and skepticism about prescription drugs is often high.

Working in an ambulatory care clinic, Dr. Strohecker noticed a “communication gap” when educating patients about warfarin. Many would return to the clinic with problems, often loaded with “pages and pages” of information on the herbal and nonherbal supplements they were taking.


“It was very, very difficult to decipher what was happening to some of these patients, and there was also a lot of antagonism to even listening to what I had to say,” she added. “They trusted their health-food store source, their chiropractor, or whoever referred them to the product, more than they trusted me.”

Users of supplements need to be more open to the risks of supplements and benefits of prescription drugs. And, healthcare professionals need to learn skills that cut through their bias and that of their patients.

1/31/11 20:43 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.