ATLANTA, United States (AFP) -- Aspirin remains the drug of choice to reduce the risk of heart disease, researchers said.

Researchers made the conclusion in a study evaluating whether taking aspirin with the blood-thinning drug Plavix diminishes the risk of having a heart attack or stroke.

The study, presented here at the American College of Cardiology's annual congress, found that taking a combination of Plavix and aspirin made little difference and could actually harm patients, like smokers or diabetics, who are most at risk of developing heart disease.

"The overall findings of this study were negative, but a benefit was seen in patients with established cardiovascular disease ... with a modest reduction of the risks," said study co-author Deepak Bhatt.

"There is no reason to use the combination therapy for primary prevention, whereas it might be useful in patients who have already had a heart attack or stroke," said Bhatt, associate director of the Cleveland Clinic Cardiovascular Coordinating Center.

The 28-month study was conducted among 15,600 people more than 45 years old.