Doctors should stop giving aspirin to ward off heart attacks in patients without cardiac disease, claim scientists.
British researchers behind the biggest study of its kind warn the tablets can harm the ‘worried well’ by raising the risk of stomach bleeding.
At the same time, it has no effect on deaths from heart problems or cancer, they said.
Aspirin: The pills, normally taken for light pain relief, are widely taken by people for their positive effects on cardiovascular health
But the scientists stress that patients with heart problems must keep taking aspirin as evidence that it prevents further attacks is indisputable.
Thousands of others who have not had a heart attack or stroke are prescribed low-dose aspirin in line with guidelines as they are feared to be at risk of cardiac attack.
In addition, healthy middle-aged people – the so-called worried well – regularly take aspirin bought over-the-counter at pharmacies in the hope it will benefit them.
Taking daily aspirin is known to cut the risk of repeat heart attacks and stroke by up to a third. But there has been uncertainty over whether it has the same benefit in patients who have never suffered an attack.
The latest study reviewed nine clinical trials involving more than 100,000 people without a history of cardiovascular disease. It found the risk of internal bleeding from aspirin cancels out any benefits to the heart.
Double edged sword: Aspirin can cut the risk of heart attacks by 10 per cent, but was found to raise the risk of dangerous internal bleeding by 30 per cent
Half of the patients took aspirin and half took an inactive substitute for an average of six years.
Taking aspirin daily, or every other day, cut the risk of heart attacks and strokes by 10 per cent, mainly due to a drop in non-fatal heart attacks. But there were no reductions in deaths from heart attacks or the number of strokes.
Doctors should consider aspirin treatment on a 'case-by-case basis' for low-risk patients
However, the benefit to the heart was almost entirely offset by a rise in the risk of internal bleeding affecting the stomach or brain.
Although one heart-related event was averted for every 120 people taking aspirin, one in 73 suffered bleeding during the same period.
Lead author Dr Rao Seshasai said people with a history of heart problems must not stop taking aspirin.
He said: ‘However, the benefits in those not known to have these conditions are far more modest than previously believed. In fact, aspirin may potentially result in considerable harm due to major bleeding.’
He said doctors should consider aspirin treatment on a ‘case-by-case basis’ for low-risk patients.
The study, published online in the Archives of Internal Medicine journal, was carried out by a team from Professor Kausik Ray’s group at St George’s, University of London.
It adds to growing evidence that giving aspirin where patients do not have symptoms of heart disease is counter-productive. A report in the Drug and Therapeutics Bulletin in 2009 said the practice should be abandoned.
And a UK study also in 2009 found aspirin can double the risk of dangerous internal bleeding in those without a history of heart disease while having no effect on the rate of heart attacks or strokes.
Natasha Stewart, senior cardiac nurse at the British Heart Foundation, said: ‘People who don’t have diagnosed heart disease shouldn’t take aspirin as the risk of bleeding may outweigh the benefits.’
Nick Henderson, executive director of the Aspirin Foundation, said the study was ‘at odds with so much existing medical opinion’.