Long term use of aspirin to prevent heart problems carries an increased risk of gastrointestinal bleeding, according to a study published in the British Medical Journal. Furthermore, no evidence exists that reducing the dose or using expensive "modified release" formulations of aspirin would reduce the likelihood of bleeding.

Researchers at the Radcliffe Infirmary in Oxford, England analysed 24 previous studies of aspirin, involving almost 66,000 patients, to establish the risk of gastrointestinal bleeding from long term treatment with aspirin. Bleeding occurred, on average, in 2.5% of patients taking aspirin compared with 1.4% who were not.

Given the widespread use of aspirin for the prevention of heart problems, these findings have important implications for daily practice, said the authors. Patients and doctors need to consider the trade-off between the benefits and harms of long term treatment with aspirin, they concluded.

In an accompanying editorial, Martin Tramr argues that we do not know who should be given what dose of aspirin and for how long. Physicians have been treating their patients with low-dose aspirin on the understanding that they did more good than harm, yet innovative research is needed to estimate rare events with confidence, he noted.