Drugmaker Merck & Co. is suspending its sale of the cholesterol drug Tredaptive after initial results from a study showed that it wasn’t effective and could raise the risk of some serious side effects.

The Whitehouse Station, N.J., company said Friday it is telling doctors to quit prescribing the tablets, which are not approved in the United States, and it also is advising patients to stop taking the medication only after talking to a physician.