8. It may protect against Parkinson's disease. A 2007 study published in Neurology suggests that women who used aspirin regularly (defined as two or more times a week for at least a month at any point in their lives) may be 40 percent less likely to develop the disease.
9. It may prevent asthma in middle-aged women. A 2008 study published in Thorax found that women 45 and older who took 100 mg of aspirin every other day were 10 percent less likely to develop asthma over the next decade than women given a placebo. The study authors noted that aspirin could exacerbate symptoms in about 10 percent of people already diagnosed with asthma.
10. It may provide zero protection against heart attacks in people with diabetes. In 2008, the British Medical Journal published research that suggests diabetics taking aspirin to prevent a first heart attack are no less likely to experience an attack than those taking a placebo. People with diabetes are at least twice as likely to develop heart disease or have a stroke as the general public.
11. It may offer no protection to some sufferers of heart attack or stroke. A 2008 research review published in the British Medical Journal found that nearly 30 percent of people with cardiovascular disease who took prescribed aspirin were resistant to its effects. Such "aspirin resistance," the study found, makes such patients four times as likely as those for whom aspirin had an effect to have a heart attack, stroke, or die.
12. It may be less effective in preventing heart attack death in women. In 2008, a research review published in the journal BMC Medicine found that earlier studies showed a large benefit in men taking aspirin to reduce the rates of fatal heart attack, but women did not receive the same advantage. A 2009 U.S. Preventive Services Task Force recommendation suggests some women may benefit from aspirin's action against ischemic strokes, however.
13. It may cause stomach troubles. People taking aspirin or another NSAID are at higher risk of gastrointestinal bleeding and stomach ulcers—particularly with long-term use of the drug.
14. It may increase the risk of bleeding. Aspirin makes the blood's platelets less sticky, and the blood less likely to clot. This is especially risky if bleeding occurs in the brain, which can be fatal.
Updated on 3/21/2012: This story is an updated version of a previously published article.