Patients with a history of heart disease who stop taking prescribed aspirin are nearly two-thirds more likely to have a heart attack, researchers have found.

A study published online by the British Medical Journal found that people who had been taking low dose aspirin to help prevent blood clots forming but then stopped were at a 60 per cent greater risk of a non-fatal heart attack.

Up to half of long-term users are believed to stop taking aspirin.

An international team of researchers from Spain and Sweden led by Luis Garcia Rodriguez examined data on 39,513 patients from The Health Improvement Network, a database of UK health records.

The patients were 50 to 84 and had been prescribed aspirin between 2000 and 2007. They were followed up for around three years.

The researchers found that in the space of a year, for every 1,000 patients there were four more non-fatal heart attacks among those who had recently stopped taking their low dose aspirin than those who had continued.

The team concluded: “Reducing the number of patients who discontinue low dose aspirin could... have a major impact on the benefit obtained with low dose aspirin in the general population.

“Research is now needed to evaluate whether efforts to encourage patients to continue prophylactic treatment with low dose aspirin will result in a decrease in non-fatal myocardial infarction.”

Ellen Mason, senior cardiac nurse at the British Heart Foundation, said: “This research is yet another reminder of how effective a little daily pill of aspirin can be at preventing someone from having another heart attack.

“So it’s very concerning how many people with heart disease are not taking their aspirin.”