Millions of people - including a substantial number of the "worried well" - take a daily dose of the drug in the belief it will keep them healthy.
But at a conference for leading doctors, British scientists said they have found that for healthy people taking aspirin does not significantly reduce the risk of a heart attack.
At the same time they found it almost doubles the risk of being admitted to hospital due to internal bleeding.
The findings show that for otherwise healthy people the risks of taking aspirin outweigh the benefits. The doctors stressed that patients who had already suffered a heart attack should continue to take the drug.