Anticoagulants prevent strokes by thinning the blood and preventing clots from forming in the heart in patients with atrial fibrillation, which can increase the risk of bleeding. It is important to seek medical help right away if you develop signs or symptoms of bleeding while taking anticoagulants: 1. abnormal bleeding, such as bleeding from a cut, non-stop nosebleeds or more bleeding than usual from brushing your teeth; 2. abnormal bruising; 3. increased menstrual flow or abnormal vaginal bleeding in women; 4. blood in the stool or black color; 5. bloody, red or dark brown urine; 6. abdominal pain or swelling; 7. headache Blurred vision, weakness, slurred speech, fainting or abnormal pallor.