Taking aspirin before non-cardiac surgery does most patients more harm than good, says an Australian anaesthetist involved in a 23-country study.

It does not prevent heart attacks and it causes bleeding, says Professor Kate Leslie.

Millions of people in Australia and New Zealand undergo non-cardiac surgery every year and, until now, around 20 per cent have been advised to take aspirin.

This is a dramatic change and will lead to new medical guidelines, says Prof Leslie, who led the Australian part of the 10,000-patient study published in the New England Journal of Medicine.

The results also show doctors should not prescribe the blood pressure drug clonidine as a preventative measure before surgery.

The study does not offer new advice for patients undergoing heart surgery or question the everyday benefits of aspirin.

“We recommend patients stop taking aspirin three or more days before surgery that is not on the heart,” says Prof Leslie.

“They can start taking it again about five days after their operation.”

However, Prof Leslie notes that a minority of people might benefit from aspirin if they are at high risk of clotting or having a stroke around the time of surgery.

Although the research settles confusion about the benefits of aspirin and clonidine, it does not offer a solution for the 10 million people worldwide who suffer a heart attack during or after an operation every year.

“Doctors do not yet have a safe and effective method of preventing these serious events,” says Dr Leslie.