"Cranberry juice contains vitamin K, which can potentially counteract warfarin's effects," Dr. Jason Singh, Chief Medical ...

Cranberry helps promote oral health because ... They also contain vitamin C, vitamin K, manganese, vitamin E and other antioxidants like phenolic acids, anthocyanins and flavonoids.

There have been reported cases in which drinking a lot of cranberry juice whilst on warfarin has caused problems, possibly because Vitamin K in cranberries affects the way warfarin works.