Eli Lilly says U.S. regulators have rejected its much-anticipated pill for the immune disorder rheumatoid arthritis, the drugmaker's second drug development setback since November.

The Food and Drug Administration said in a letter to the company that additional data from patient tests would be needed to better understand safety concerns and to determine the most appropriate doses, Lilly announced Friday. Lilly said it will work with the FDA on a plan to eventually get the drug, baracitinib, approved for U.S. patients.

In November, Lilly's experimental Alzheimer's medicine flopped in a closely watched patient test.

The drug, which has the proposed brand name Olumiant and is approved for use in Europe, was expected to be a big seller in part because most other new rheumatoid arthritis drugs are injected.