Warfarin (Coumadin) is a medication commonly prescribed to prevent blood clots, especially in patients with atrial fibrillation. Patients who take warfarin must get periodic tests to check on the clotting status of their blood to make sure that drug's action is neither excessive nor inadequate to prevent clots from forming.
Five frequently used herbal supplements, all beginning with the letter "g," can alter the action of warfarin. Three of them - garlic, ginger, and gingko biloba - can increase the danger of bleeding by enhancing the anticoagulant action of warfarin. The other two - ginseng and goldenseal - can decrease its anticoagulant effect and raise the risk of a blood clot if taken in large amounts on a regular basis.
Several other herbal supplements can alter the effects of warfarin. Feverfew, fenugreek, and chamomile can enhance warfarin's action, and St John's wort can reduce its effectiveness in preventing clots.
Several antibiotics and large doses of acetaminophen (Tylenol), among other drugs, can also increase the anticoagulant effects of warfarin. Patients are often told to avoid these drugs when they are taking warfarin, but they may not be warned or concerned about a risk from dietary supplements.
Patients should also recognize that dark green vegetables and avocados contain large amounts of vitamin K, which also can interfere with the anticoagulant effect of warfarin.
The effects of these herbs and nutrients on warfarin are just examples of the hidden potential dangers of dietary supplements. Make sure to tell your doctor about all other medications and supplements you are taking.
By Simeon Margolis, M.D., Ph.D. Provided by : Johns Hopkins University
