Patients with osteoarthritis face a higher risk of heart problems if they take ibuprofen, a common painkilling medicine.
The study compared cardiovascular health in 18,000 people with osteoarthritis who were taking either lumiracoxib which is a type of COX inhibitor, ibuprofen or naproxen.
One in ten of the patients were considered to be at high risk of heart attack and some took aspirin daily.
Patients at high risk of developing cardiovascular disease and taking ibuprofen were found to be around nine times more likely to have heart attacks or strokes than those taking lumiracoxib.
The pattern did not emerge among those classified as low risk of heart problems.
Patients taking ibuprofen were also found to develop congestive heart failure more often than those taking the COX inhibitor.
The study also found signs that ibuprofen interferes with the blood thinning properties of aspirin in patients at high risk of cardiovascular disease.