Merck, a major U.S. pharmaceutical company, announced this week that its drug “Tredaptive” has failed a clinical trial. The trial was meant to test the drug for its ability to improve patients’ heart health by increasing their levels of “good” cholesterol.

The trial, conducted at Oxford University and funded by Merck, looked at 25,673 patients at high risk for heart attack. The patients were given either Tredaptive or placed on standard stating therapy and followed for a median of 3.9 years.

Researchers found that the drug did not reduce the patients’ risk for heart attacks, strokes, necessary bypass surgeries, or death due to heart attack. Worse still, patients in the trial were found to have an increased risk for “serious,” though non-fatal, side effects.

“While we are disappointed in these results, we thank the investigators who have conducted the study and the patients who have participated in it,” said Peter Kim, president of Merck Research Laboratories. “We are committed to working closely with the independent research team at Oxford University and with regulatory agencies to understand the results and determine next steps.”

Tredaptive, also marketed as Cordaptive, Pelzont, and Trevaclyn, is already approved in around 70 countries, including some in Europe. It is already sold in around 40 countries, and saw $13 million in sales during the first three quarters of 2012. Merck is now sharing the results of the trial with regulators in the countries where the drug is approved.