Low-dose aspirin should not routinely be used to prevent heart attacks and strokes, contrary to official guidance, say UK researchers.
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, they found. The Lancet study should help clarify a "confusing" issue, GPs said.
The NHS drugs watchdog, the National Institute for health and Clinical Excellence (NICE), has not made a ruling in this area. But experts in the UK, US and Europe recommend aspirin for people who have not already had a heart attack or stroke, but are at high risk of cardiovascular disease because of factors such as age, blood pressure and cholesterol level.
This strategy, known as primary prevention, is based on the result of studies looking at predicted risks and benefits in this population. But the latest research provides clearer evidence because it is based on data from individuals, the researchers said.
They looked at heart attacks and strokes and major bleeds - a potential side effect of aspirin - in six primary prevention trials, involving 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, with no difference in the risk of stroke or deaths from vascular causes. But it also increased the risk of internal bleeding by around a third.