Aspirin has long been recognised as a drug that can help protect against adverse heart events, such as heart attacks and stroke. However, Irish scientists have discovered the commonly used drug may be ineffective in preventing recurrent heart attacks in as many as one in five people.

Aspirin protects against heart events by reducing the risk of clots developing in blood vessels. It is often taken by people who have already suffered an adverse event, such as a heart attack. These patients are at a higher risk of suffering another heart attack compared to people in the general population.

However research carried out by the Irish Heart Foundation's National Cardiovascular & Stroke Research Network (NCSRN Ireland) found that in 20% of patients taking aspirin as a preventative medicine, it may be ineffective.

The research was carried out in eight hospitals in Dublin, Cork and Galway and involved over 700 patients with heart disease.

It found that patients with the highest risk of an inadequate response to aspirin therapy were younger men - those in their 40s - with diabetes and high blood pressure, who may also be obese and consume high amounts of alcohol.

"The profile of the patients who are not adequately protected are typically men with high blood pressure, overweight and with a high alcohol intake. This group, who are at high risk of recurrent heart attack, are not getting the benefit of a cheap and generally effective therapy," explained lead researcher, Prof Dermot Kenny, of the Royal College of Surgeons in Ireland.

He said that the findings indicate that about 20% of the 700 people in the study ‘are not protected by their existing therapy'.

Commenting on the findings, Dr Angie Brown, medical director of the Irish Heart Foundation, described them as ‘significant'.

"They point to the critical role of clinical research in identifying this ‘at risk' group of patients. We hope it will drive the establishment of new approaches to allow for accurate identification and management of this ‘at risk' cohort of patients in secondary prevention," she said.

She added that further research was needed to explore if these findings ‘amount to an adherence issue or a pharmacological resistance to aspirin'.

In 2011 alone, over 5,500 people were discharged from hospital having suffered a heart attack and more than 2,100 people died as a result of an attack. NCSRN Ireland was established in 2011 by the Irish Heart Foundation and it is made up of doctors and scientists specialising in the fields of heart and stroke.

The findings of this study will be presented at the Irish Cardiac Society's Annual Scientific Meeting in Killarney later this week.

For more information on heart health, see our Heart Disease Clinic here