Aspirin is not an advisable investment for healthy women who are looking to prevent heart attacks or stroke, state Dutch researchers.
They said 50 women would need to take the medication for 10 years for just one to be helped - assuming they are all at high risk to begin with.
"There are very few women who actually benefit," the Daily Mail quoted Dr Jannick Dorresteijn of University Medical Center Utrecht in The Netherlands, as saying.
"If you don't want to treat 49 patients for nothing to benefit one, you shouldn't treat anyone with aspirin."
The new study adds to a long-standing controversy over aspirin, one of the world's most widely used drugs. Common side-effects include irritation of the stomach or bowel, heart burn and nausea.
Doctors agree it's worth taking for people who've already had a heart attack or a stroke, but they are less certain when it comes to so-called primary prevention.
'We all appreciate that the average treatment effect is very small, but that some patients may benefit more than others," Dr Dorresteijn said.
Today, aspirin is highly recommended for people at increased risk for heart problems.
But the Dutch findings suggest many women would still be taking the drug needlessly.
The team analysed data from nearly 28,000 healthy women aged 45 and above who had received either aspirin or dummy pills in an earlier U.S. trial.
The women on aspirin generally took a low dose of 100mg every other day.
Overall, aspirin cut the rate of heart attacks, strokes and death from heart disease from 2.4 per cent to 2.2 per cent.
"Nine out of 10 women experience less than a one-percent risk reduction for cardiovascular disease in the next ten years, so that is a really small treatment effect," Dr Dorresteijn said.
The study has been published in the European Heart Journal.