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

Yes, drinking Grape Juice can potentially increase INR levels in individuals taking Coumadin (warfarin). Grape juice contains compounds that can inhibit cytochrome P450 enzymes, which are involved in the metabolism of warfarin. This inhibition can lead to higher concentrations of warfarin in the bloodstream, resulting in an increased INR and a greater risk of bleeding. It's advisable for patients on warfarin to consult their healthcare provider before consuming grape juice or similar products.