Most people at increased risk of having a heart attack or stroke take a low dose aspirin (75 mg) each day. This reduces the risk of having a heart attack by about a third, and the risk of having a stroke by about a quarter. However, there is a small risk of serious side-effects with aspirin. In particular, bleeding from the gut. If you develop upper abdominal (tummy) pains, pass blood or black stools, or vomit blood, then stop taking the aspirin and see your doctor as soon as possible or go to the nearest casualty department.A daily dose of aspirin 75mg can reduce the risk of cancer and prevent the disease from spreading, studies show.