Incyte Corp. says a study of an experimental pill developed with Eli Lilly and Co. for rheumatoid arthritis showed the drug reduces inflammation in patients’ joints at all doses.

At the highest dose of 10 milligrams, 72 percent of patients taking the drug daily had a 20-percent reduction in joint swelling after 24 weeks, 44 percent had a 50-percent drop and 28 percent had a 70-percent decline, Wilmington, Del.-based Incyte said in a prepared statement. By comparison, 32 percent of patients taking placebos had a 20-percent drop in inflammation, 13 percent had a 50-percent decline and 3 percent had a 70-percent drop, the company said.

The drug, previously known as INCB28050, will be called LY3009104, and Indianapolis-based Lilly will be responsible for future clinical trials, Incyte said in its statement. Headache, upper respiratory tract infections, and diarrhea were the most frequently reported side effects mentioned by the 125 patients who took part in the study, the company said.

Lilly paid $90 million in 2009 to acquire the global rights to the treatment in a bid to beef up its pipeline of medications for autoimmune diseases. If the drug makes it to market, Lilly could pay another $665 million to Incyte for reaching various milestones along the way.

The latest study results suggest that “the compound has the potential to become a welcome addition” to current therapies, said Maria Greenwald, a Palm Desert, Calif., rheumatologist who led the study. The findings were released Thursday at the American College of Rheumatology meeting in Atlanta.

In rheumatoid arthritis, the body’s immune system attacks itself, causing joint inflammation and swelling that can lead to progressive destruction of the joints. The disease affects about 1 percent of the world’s population.

The pill is one of a family of experimental treatments for rheumatoid arthritis targeting a protein called JAK that leads to joint destruction. Pfizer Inc. also reported results showing an experimental JAK-targeted medicine that reduced pain and inflammation in a trial released at the rheumatology meeting.

Three biotechnology companies are developing JAK drugs: Incyte, Rigel Pharmaceuticals Inc. of San Francisco, Calif., and Cambridge, Mass.-based Vertex Pharmaceuticals Inc.