Taking a daily dose of aspirin to prevent a heart attack or stroke may do more harm than good, scientists including one of an Indian-origin have warned.
Aspirin has previously been hailed as a "wonder drug" and come to be regarded as a "just in case" self-medicated measure for millions of healthy patients.
Experts had recommended everyone over the age of 45 to consider taking a daily dose of aspirin because it can reduce the risk of a heart attack or stroke and prevent some cancers.
But British researchers called for guidelines to be revised after they found the risk of internal bleeding outweighed potential benefits.
In a study of 100,000 healthy people who have taken aspirin, the largest of its kind, they found that the drug reduced the risk of heart attacks by about 10 per cent but the risk of "non-trivial" bleeding rose by a third.
The findings suggested that, while one heart attack or stroke was averted for every 120 people treated with aspirin over a six-year period, one in 73 people suffered potentially significant bleeding.
The researchers at St George's, University of London, recommended that people who have suffered a heart attack or stroke and are therefore at a high risk of another should still be routinely prescribed aspirin.
However, they raised concerns about the millions of otherwise healthy people who are taking aspirin in an attempt to prevent first heart attack or stroke.
"The beneficial effect of aspirin on preventing future cardiovascular disease events in people with established heart attacks or strokes is indisputable. We urge people with these conditions not to discontinue their medication unless advised to do so by their physicians for valid reasons," the Sydney Morning Herald quoted lead author Professor Kausik Ray as saying.
"However, the benefits of aspirin in those individuals not known to have these conditions are far more modest than previously believed and, in fact, aspirin treatment may potentially result in considerable harm due to bleeding.