The agency says it hasn't yet seen data from the study questioning the effectiveness of Zetia, one of the components of Vytorin.
However, it felt it was important to give doctors and patients guidance.
Last week, Merck and Schering-Plough, which market Vytorin, reported that a trial showed that Zetia did not reduce heart attacks or strokes any better than the conventional stain drugs.
Zetia's marketing contends it lowers cholesterol in a different way, while ads for Vytorin say that because it combines Zetia with a statin, Zocor, it is more effective.
During a tele-conference, FDA officials said until it reviews the data, patients and doctors should keep the existing data in mind - that there are no studies yet showing that either drug cuts heart attacks or strokes.
An ongoing clinical trial of Vytorin will likely be completed in 2011.
