Although the commercial fallout from any decision to pull the drug from the market in Europe would be limited, it would be a blow to Merck's reputation.
Bernstein analyst Tim Anderson estimates that Tredaptive sales in Europe and other non-U.S. markets are running at only around $50 million a year, compared to Merck's overall revenue of $47 billion.
The drug is designed to raise "good" HDL cholesterol but the 25,000 patient study found it didn't do better at preventing heart attacks, deaths or strokes than traditional statin drugs that lower "bad" LDL cholesterol.
The large-scale trial also found that patients taking the drug suffered more non-fatal but serious side effects than those only taking statins.
The medicine was approved for use in Europe in 2008, but U.S. regulators were unwilling to approve it until Merck conducted the costly long-term study to better assess its safety and effectiveness.
Merck said on Thursday that it no longer planned to seek regulatory approval for the drug in the United States and recommended that doctors did not start new patients on Tredaptive in countries where it is already available.
The regulator backed that advice on Friday, but added that patients currently using the drug should speak a doctor at their next appointment but not stop their treatment.
Tredaptive is sold under the brand name Pelzont in Italy and Trevaclyn in both Italy and Portugal. A decision on the future of the drug in Europe is expected in January.
(Reporting by Chris Wickham; Editing by Elaine Hardcastle)