Healthy people who take aspirin to prevent a heart attack or stroke could be doing more harm than good, warn researchers.
An analysis of more than 100,000 patients, published in Archives of Internal Medicine, concluded the risk of internal bleeding was too high.
The UK-led study said only people with a history of heart problems or stroke should take the tablets.
Experts said any decision should be made with a doctor.
Aspirin helps people who have had a heart attack or stroke. It prevents blood clots from forming by preventing cells, known as platelets, from sticking together. By reducing the number of clots formed, the tablets reduce the risk of another heart attack or stroke.
There have also been suggestions that the drug can prevent some cancers, however, the drug is known to increase the chance of internal bleeding, including bleeds on the brain.
The discussion has been whether at-risk or even healthy people should also take aspirin.