People who take an aspirin a day to prevent heart attacks could be doing more harm than good.
Many diabetics currently take the drug to counter the risk of heart attacks.
But a major trial found taking aspirin had no benefits for people without any symptoms of heart disease — and it can cause bleeding in the stomach.
However research by the British Medical Journal revealed there are still groups of people who would benefit from taking aspirin.
The study found that aspirin benefited people who have already suffered a heart attack or stroke as the drug could reduce the risk of future related problems by a quarter.
The research said the drug was most effective if prescribed to people with more serious cardiovascular problems.
"If you're taking aspirin for secondary prevention because you've had a heart attack, or stroke, or have a circulatory problem, then it works," said study leader Professor Jill Belch of Dundee University. "But it doesn't work if you have none of these problems and there is also no evidence for its use by healthy middle-aged people.”
The study involved more than 1,200 middle-aged patients with type one or type two diabetes.