Analysis of data from over 100,000 clinical trial participants found the risk of harm largely cancelled out the benefits of taking the drug.

Only those who have already had a heart attack or stroke should be advised to take a daily aspirin.

The Lancet study should help clarify a "confusing" issue, GPs said.

Professor Colin Baigent, study leader said: “We don't have good evidence that, for healthy people, the benefits of long-term aspirin exceed the risks by an appropriate margin.”

The study looked at heart attacks and strokes and major bleeds – a potential side effect of aspirin – in six primary prevention trials.

They involved 95,000 people at low to average risk and 16 trials involving 17,000 people at high risk - because they had already had a heart attack or stroke.

Use of aspirin in the lower-risk group was found to reduce non-fatal heart attacks by around a fifth.

But it also increased the risk of internal bleeding by around a third.