And this is exactly the sort of crazy nonsense that happens when you give medical information to laypeople without explaining it properly. Warfarin doesn't cause strokes, or if it does, it does so as a crazy and crazy unlikely side-effect in a vanishingly small number of patients. The common, dangerous, life-threatening side effect of Warfarin, the one you need to be worried about with a Warfarin sensitivity, is bleeding. Of course, Warfarin, when administed in a careful, low dosage to people with the sensitivity, may fail to prevent a stroke, but Warfarin almost certainly did not give the previous commenter's grandma a stroke, and it's driving me slightly crazy that this thread is causing people to think that it's some sort of common side effect.