Aspirin, that old standard in everyone's medicine chest, can really pack a wallop. So much so that the American Heart Association has long recommended aspirin therapy for people who've had a heart attack, stroke caused by blood clot, unstable angina, or "ministrokes." The AHA also notes that even people who have not experienced such an event but who are at increased risk because of family history, say, may also stand to gain from aspirin therapy.

We're certainly familiar with our aspirin: About 60 percent of people ages 65 and older pop aspirin at least once a week. But this cheap, over-the-counter pill is not benign, and regular use should be discussed with a doctor. And beware marketing claims. Bayer was sent warning letters by the Food and Drug Administration today for touting two products—Bayer Women's Low Dose Aspirin + Calcium (Bayer Women's) and Bayer Aspirin with Heart Advantage (Bayer Heart Advantage)—for making unproved health claims.

Along with its benefits, aspirin has limitations, too. A roundup of recent research suggests taking aspirin regularly may do the following:

1) Cut pre-eclampsia risk during pregnancy. A research review published in The Lancet in 2007 suggests that pregnant women who took aspirin or other antiplatelet drugs were 10 percent less likely to develop the disorder that involves high blood pressure and potentially serious complications for mother and fetus. Aspirin therapy during pregnancy should definitely be discussed with an obstetrician.

2) Reduce risk of developing colorectal cancers. The journal Gastroenterology published a study earlier this year that found a significantly lowered risk of developing the cancers in men with regular, long-term aspirin (and other nonsteroidal anti-inflammatory) use. The benefits, however, were not evident until individuals had amassed a total of five consistent years of regular use. Also, the dose with the biggest benefit—325-mg pills more than 14 times each week—is greater than typically recommended.

3) Lower a woman's risk of breast cancer. A research review published this month in the Journal of the National Cancer Institute found a 13 percent relative risk reduction in women who used aspirin regularly compared with those who did not. The findings found an overall reduced risk of 12 percent for regular use of NSAIDs in general. Previous research on breast cancer risk and NSAID use has shown conflicting results.

4) Throw off test results for prostate cancer. In an issue of this month's journal Cancer, researchers reported that men who used aspirin and other NSAIDs regularly had about 10 percent lower levels of the prostate marker prostate-specific antigen. The researchers suggest this may hinder the detection of prostate cancer in regular users.

5) Offer some protection against Alzheimer's disease. Research has been inconclusive, but a review published this year in the journal Neurology found people who used aspirin had a 13 percent lower risk of developing Alzheimer's. The study added to an ongoing debate about whether certain types of NSAIDs, say ibuprofen vs. aspirin, were more beneficial.

6) Help prevent strokes—unless you also take ibuprofen. A small study published this year in the Journal of Clinical Pharmacology found that stroke patients taking daily aspirin to prevent another stroke who also took ibuprofen—say, for their arthritis—reaped no antiplatelet benefit. After the patient stopped the ibuprofen, the aspirin became effective. The Food and Drug Administration warns that aspirin's benefits may be diminished by ibuprofen use.

7) Prevent asthma in middle-aged women. A study published in the journal Thorax this year 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 note that aspirin could exacerbate symptoms in about 10 percent of people already diagnosed with asthma.

8) Protect against Parkinson's disease. A 2007 study published in Neurology suggests that women who used aspirin regularly (defined as two or more a week for at least a month at any point in their life) may be 40 percent less likely to develop the disease.

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.