BMJ Group Medical Reference
Aspirin helps to prevent blood clots. Cells in your blood called platelets help your blood to clot by sticking together. Aspirin makes these cells less sticky and helps to prevent blood clots. 
We're not certain how good aspirin is at preventing strokes for people with atrial fibrillation. For people at a high risk of a stroke, aspirin doesn't seem to be as good as the drugs dabigatran or warfarin.    
Aspirin is sometimes used as an alternative for people who can't take warfarin, dabigatran or rivaroxaban. It's also used for people who have a lower risk of a stroke. 
Platelets are small disc-shaped particles found in your blood (along with red blood cells and white blood cells). Platelets form the clots that stop the bleeding when you've been cut. People who don't have enough platelets have problems with bleeding too much.
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