Tofacitinib, sold under the brand Xeljanz, Neojanz among others, is a medication used to treat rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, polyarticular-course juvenile idiopathic arthritis, and ulcerative colitis. It is a janus kinase (JAK) inhibitor, discovered and developed by the National Institutes of Health and Pfizer.