XELJANZ, also known by its generic name tofacitinib, is a prescription medication that belongs to a class of drugs known as Janus kinase (JAK) inhibitors. It is designed to interfere with the JAK pathways, which are involved in the immune system's activity. By doing so, XELJANZ helps to reduce inflammation and modulate the immune response. It is primarily used in the treatment of moderate to severe rheumatoid arthritis, psoriatic arthritis, and ulcerative colitis in adults who have not responded well to traditional therapies. XELJANZ works by targeting specific enzymes in the body, helping to relieve symptoms, improve physical function, and possibly slow the progression of joint damage in patients with arthritis. Like all medications, it can have side effects, and its use must be closely monitored by a healthcare provider.