A blood thinner being developed by Merck has flopped in a major study aimed at preventing heart attacks, strokes and other problems in people who had suffered a heart attack or severe chest pain from clogged arteries.

The drug, vorapaxar, (vor-uh-PACKS'-ar), gave no significant benefit when added to standard medicines in a study of 13,000 patients around the world. It also raised the risk of serious bleeding. Merck officials say results due out early next year from another large study testing the drug in different types of patients will tell more about its potential.

Results were reported Sunday at an American Heart Association conference in Florida.