The possible side affects of aspirin must be examined before it can be widely used as a cancer prevention method, the charity Cancer Research UK has said.
A new study suggests people who take a daily dose of aspirin could significantly reduce their risk of cancer.
"Aspirin is showing promise in preventing certain types of cancer, but it's vital that we balance this with the complications it can cause - such as bleeding, stomach ulcers, or even strokes in some people," Dr Julie Sharp, head of health information at the charity said.
"Before aspirin can be recommended for cancer prevention some important questions need to be answered, including what is the best dose and how long people should take it for. And tests need to be developed to predict who is likely to have side effects."
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