People who take warfarin—long a mainstay for treating atrial fibrillation—may need to stay extra vigilant to make sure their blood levels of this drug stay in a safe but effective range. Warfarin works by blocking the production of substances in the blood known as clotting factors. Many common drugs, foods, and dietary supplements affect warfarin, so the same dose may cause either too much or too little anti-clotting effect at different times. And warfarin users who have health-related changes should stay in close contact with their doctors about possible additional blood testing.
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