Will Cranberry Juice Interact with Coumadin (warfarin)?

My husband may have a kidney infection and I want to give him cranberry juice, but he is on Coumadin. Would this affect his medicine?

The Health meets Food Team Says...

Updated!

New evidence shows that cranberries and cranberry juice are OK for those on Coumadin (warfarin) Read more...

Interestingly, a cup of cranberry juice cocktail has only 2.5 micrograms (mcg) of Vitamin K. There have been some case reports that cranberry juice can have an effect on INR levels, however.

One report in the British Medical Journal in 2003 is concerning. The patient in question was drinking a great deal of cranberry juice and on an essentially liquid diet. There is a cautionary statement by the British Government about drinking cranberry juice while on Coumadin as a result of some other case reports. There have not been any such case reports that I have found in North America.

Thanks for writing.