Healthy people who take aspirin to prevent heart attacks could be doing more harm than good, experts said.
Many people are thought to take a daily dose of the drug in the hope it will help prevent heart trouble.
But the Aspirin for Asymptomatic Atherosclerosis (AAA) trial found its routine use to prevent vascular problems "cannot be supported".
A recent Lancet study said low-dose aspirin should not routinely be used to prevent heart attacks and strokes.
Professor Peter Weissberg, of the British Heart Foundation which part-funded the latest research, said: "We know that patients with symptoms of artery disease, such as angina, heart attack or stroke, can reduce their risk of further problems by taking a small dose of aspirin each day.
"The findings of this study agree with our current advice that people who do not have symptomatic or diagnosed artery or heart disease should not take aspirin, because the risks of bleeding may outweigh the benefits."
The Asprin Foundation, which offers advice on the use of asprin, said there was an existing, strong body of evidence supporting the use of low-dose aspirin to help prevent heart trouble in appropriate patients.
It said such aspirin use was only appropriate where individual patients were "considered by their doctor to be at special risk from particular factors such as obesity, lifestyle, stress and a familial history."
It said people should seek medical advice before taking asprin in this way.
The AAA trial recruited 28,980 men and women aged 50 to 75 years in central Scotland, who were free of clinically evident cardiovascular disease.
The study was led by Professor Gerry Fowkes from the Wolfson Unit for Prevention of Peripheral Vascular Diseases in Edinburgh.
The results were presented at the European Society of Cardiology Congress in Barcelona.