The move was seen in investor anxiety about the future of prasugrel, a blood-thinning drug, the Indianapolis Star said.

The Indianapolis-based Lily said it was suspending two small clinical trials of prasugrel because it needed to adjust doses in certain patients.

Analysts and investors have called prasugrel Lilly's most critical late-pipeline drug, a potential blockbuster that could help shore up the company's revenues in coming years. Lily has been losing patents on several other major drugs, including Zyprexa and Gemzar.

Some analysts wonder whether the latest development means bigger trouble for prasugrel, which Lilly is trying to show is superior to a established blood thinner, Plavix, made by Bristol-Myers Squibb, the Star said.

Lilly said the suspension of the smaller trials "should not be interpreted to represent the outcome" of the larger study.