Millions of healthy older people with no history of heart attack or stroke take low-dose aspirin in the hope it will reduce their risk and prolong good health.
It was first synthesised in 1898, and since the 1960s has been known to lower the risk of heart attack and stroke among those who had previously experienced heart disease or stroke.
They said that while higher all-cause mortality was observed among apparently healthy older adults who received daily aspirin, than among those who received placebo, this was attributed primarily to cancer-related death and in the context of previous studies, this result was unexpected and should be interpreted with caution.
Over 19,000 people in Australia and the United States were studied over seven years for the study was called ASPREE-Aspirin in Reducing Events in the Elderly.
The participants were followed for around 4.7 years and could also not have dementia or a physical disability and had to be free of medical conditions.
Contrary to popular belief, an aspirin-a-day may not quite work as a preventive in older people who have not had a heart attack.
Although the study showed obvious risks of taking aspirin, McNeil remained convinced that the drug is a relatively safe medication to use.
Researchers found people taking the aspirin showed a significantly higher risk of bleeding, such as hemorrhages. Aspirin might still help some middle-aged people younger than 65, or it could have longer-reaching benefits for the elderly that would take more years to pay off, such as preventing dementia (in the current study, though, there was no difference in the dementia rate).
Experts last night urged people to take medical advice from their before deciding whether or not to use aspirin regularly.
About half of them took 100 milligrams of aspirin daily (slightly more than a baby aspirin, which has 81 milligrams) and the other half were given a placebo.
The researchers did not state whether healthy older people who have been taking aspirin should stop.
Aspirin has been widely used in healthy older adults to protect against cardiovascular disease and cancer.
"Clinical guidelines note the benefits of aspirin for preventing heart attacks and strokes in persons with vascular conditions such as coronary artery disease", Richard J. Hodes, director of the National Institute on Aging, which helped fund the research, said in a news release.
Doctor Evan Hadley, of the NIA, added: 'Continuing follow-up of the ASPREE participants is crucial, particularly since longer term effects on risks for outcomes such as cancer and dementia may differ from those during the study to date.
The minimum age was 70; 65 in the United States for African-American and Hispanic individuals due to their higher risk for dementia and cardiovascular disease.
Clinically significant bleeding - hemorrhagic stroke, bleeding in the brain, gastrointestinal hemorrhages or other hemorrhages that required transfusion or hospitalisation - occurred in 3.8 per cent on aspirin and in 2.7 per cent taking the placebo.