The most common dose of aspirin given to prevent a stroke is 81 milligrams, according to WebMD. However, some patients need to take as much as 325 milligrams of aspirin per day to prevent stroke. Doctors recommend taking aspirin only if the risk of stroke outweighs the risks of aspirin.
Low-dose aspirin is 81 milligrams, while an adult-strength aspirin typically is 325 milligrams, according to WebMD. Doctors often recommend that people who have already had a stroke take aspirin every day to prevent the risk of having another, since aspirin prevents blood clot formation in the arteries. People who have never had a stroke or heart attack should consult their doctor before starting to take a daily dose of aspirin.
Although aspirin reduces the risk of strokes that are caused by clots, it could make some strokes caused by bleeding in the brain worse, according to WebMD. Therefore, people who have recently had this kind of stroke should not take aspirin. Patients also should avoid taking aspirin if they have a stomach ulcer, are allergic to aspirin, have uncontrolled high blood pressure or have asthma that gets worse when they take aspirin. For patients who are unable to take aspirin, clopidogrel is an alternative medication for preventing stroke.