Scientific research published questioned the benefits of taking an aspirin a day to reduce the risk of an untimely death from a heart attack or stroke.
The study, the largest conducted in people with no previous history of heart problems, found that such patients were unlikely to fare better on a regular dose of the common medicine because it increases the risk of internal bleeding.
"The benefits of aspirin in those individuals not known to have these (heart) conditions are far more modest than previously believed and in fact, aspirin treatment may ... result in considerable harm due to major bleeding," said Rao Seshasai of St George's, University of London, who led the study.
It found that while one so-called cardiovascular event was averted for every 120 people treated with aspirin for about six years, one in 73 people suffered from potentially significant bleeding during in the same period.
The findings, published in the Archives of Internal Medicine journal, will fuel an already intense debate about the merits of taking aspirin, which experts say carries a risk of bleeding in the stomach in around one patient in every 1 000 per year.
Seshasai said that in the light of his findings, aspirin recommendations such as the United States Preventive Services Task Force guidelines and the Joint British Societies' guidelines should be reviewed.
Instead of broad recommendations, he said, aspirin treatment should be considered "more selectively on a case-by-case basis".
Aspirin, originally developed by Bayer, is a cheap over-the-counter drug used for pain and to reduce fever.
The drug reduces the risk of clots forming in blood vessels and can therefore protect against heart attacks and strokes, so it is often prescribed for people who already suffer with heart disease and have already had one or several attacks.
Research published last year also found taking daily aspirin had a significant protective effect against the risk of developing many types of cancer - particularly bowel cancer and other gastrointestinal tumours.
The scientist who led the cancer study said that while taking aspirin carried a small risk of stomach bleeding, that risk was beginning to be "drowned out" by its benefits in reducing the risk of cancer and the risk of heart attacks.
Many medical experts prescribe a daily aspirin dose as a precaution for people with no previous history of heart attack or stroke, but who are considered at higher risk due to other factors such as having high blood pressure or being overweight.
Seshasai's team looked at aspirin's effectiveness when used in this way - called primary prevention - and found that while daily or alternate day doses cut the risk of cardiovascular events by 10%, this was mainly due to fewer non-fatal heart attacks.
The overall reduction in the study, which analysed data from nine clinical trials involving more than 100 000 participants, was also found not to include reductions in other events such as deaths from heart attack, or fatal or non-fatal strokes.
The study showed the benefit of regular aspirin was almost entirely offset by a 30% increase in risk of life-threatening or debilitating incidences internal bleeding.
It also looked at the effects aspirin had on deaths from cancer and found that contrary to last year's study, aspirin did not reduce the overall risk of death from cancers.
"There is an enormous interest in understanding the role of aspirin in cancer prevention," Seshasai said. "No evidence of benefit was found (in this study)... but more research is needed given these were only of six years in duration."
(Sapa, January 2012)