Can drinking grape juice cause an INR to increase when taking coumadin?

Yes, drinking grape juice can cause an INR to increase when taking Coumadin.

Grapefruit juice is well known to interact with Coumadin, but grape juice has also been shown to increase the risk of bleeding in people taking warfarin. This is because grape juice contains a number of compounds that can interfere with the way warfarin is metabolized in the body. As a result, people who drink grape juice while taking warfarin may experience an increase in their INR, which can increase the risk of bleeding.

If you are taking warfarin, it is important to avoid drinking grape juice. You should also talk to your doctor about any other foods or drinks that may interact with warfarin.