Grapefruit can increase the effectiveness of warfarin by affecting it's metabolism so you should be cautious.
NO, grapefruit is NOT recommended concurrently with warfarin (brand name Coumarin). The warfarin prescribing information (aka PI: the *official*, FDA-approved information that accompanies the product) describes how the drug is metabolized by the cytochrome P450 pathway. The furanocoumarin compounds in grapefruit interfere with the enzymes in the P450 cascade. Thus, grapefruit consumption will cause warfarin to remain in your body longer (because warfarin metabolism is delayed for up to 72 hours after eating/drinking the grapefruit), and your PT/INR level will rise.
I've eaten grapefruit twice within a couple days of having my INR done, and both times my INR has been high. I've been on coumadin for 4 years and the only times my INR has been high are these two times that I've eaten grapefruit. I no longer eat it.
I am 73 I have been taking warfarin about 10 years. 5 months ago we moved into a different home. It has 2 super producer grapefruit trees, enough to supply the neighbors and all of my friends. I have eaten a fresh grapefruit (picked just before breakfast) for the entire 5 months. If anything, my INR has gone DOWN.
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