9) Provide zero protection against heart attacks in people with diabetes. This month, the British Medical Journal published research that suggests diabetics taking aspirin to prevent a first heart attack were 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.
10) Offer no protection to some sufferers of heart attack or stroke. A research review published in the British Medical Journal in January 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.
11) 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.
12) Be less effective in women. This month, 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 reap the same benefit.