The U.S. Food and Drug Administration this week approved Xeljanz (tofacitinib) for the treatment of moderate to severe rheumatoid arthritis (RA) in adults who have not responded to methotrexate.

The twice-daily pill works by blocking molecules known as “Janus kinases.” The approval was based on the medication’s approval was based on its demonstrated effectiveness and safety in seven clinical trials. In all of the trials, adults with moderate to severe RA “experienced improvement in clinical response and physical functioning” when treated with Xeljanz. The drug was, however, associated with an increased increases in cholesterol and an increased risk of serious infections, including tuberculosis, cancers, and lymphoma.

“RA is a serious and disabling disease that affects people in their everyday lives, and many patients do not adequately respond or are intolerant to currently available therapies,” said Dr. Stanley Cohen, study investigator and clinical professor of rheumatology at the University of Texas Southwestern Medical School. “In clinical trials, Xeljanz significantly reduced the signs and symptoms of RA and improved physical function. As a physician, I am pleased that we have another choice for patients living with inadequately controlled, moderately to severely active RA.”

According to the FDA, RA is an autoimmune disease in which the body’s immune system attacks healthy tissue, leading to the inflammation of joints. The U.S. Centers for Disease Control and Prevention (CDC) estimates that it affects 1.5 million Americans.

Xeljanz was developed by Pfizer, and the company has agreed to conduct post-marketing clinical trials to evaluate the long-term safety of the drug.