Even people with atherosclerosis—where the arteries are already narrowing or hardening—aren't helped by taking aspirin, say researchers from the University of Florida.
The discovery throws into question standard advice, extolled by cardiologists and doctors around the world, that taking an aspirin a day should be part of everyone's routine health regime to prevent heart disease.
As a result, aspirin has become the world's most popular drug, and its use as a preventative of heart disease has far outstripped its original purpose as a painkiller.
But when the researchers tracked the health of more than 33,000 patients with atherosclerosis, they discovered that aspirin made no difference as to who among them would go on to suffer a heart attack or stroke.
Even the 21,000 or so who had already had a heart attack saw only the smallest benefit from taking the drug; the risk of heart disease, heart attack or stroke was 10.7 per cent among aspirin users and 10.5 per cent among non-users.
The only people who should carry on taking aspirin were those who had had a coronary by-pass or had a stent fitted to widen the arteries. It's also an effective therapy in the moments when someone is suffering a heart attack or stroke.
And because aspirin can increase the risk of stomach bleeding and even bleeding in the brain, it shouldn't be a drug that people take routinely, the researchers conclude.