In a phase 3 randomized trial of 1307 patients with rheumatoid arthritis receiving background methotrexate, the oral JAK1 and JAK2 inhibitor baricitinib showed superior efficacy to placebo and to the anti–tumor necrosis factor α monoclonal antibody adalimumab. Rheumatoid arthritis is a systemic autoimmune disease characterized by inflammatory synovitis and progressive joint destruction, which are associated with severe disability and increased mortality. Progress in treatment with the use of conventional synthetic disease-modifying antirheumatic drugs (DMARDs), such as methotrexate, and biologic DMARDs that target tumor necrosis factor (TNF) has made clinical remission a realistic target. 1 Activated Janus kinases (JAKs) play pivotal roles in intracellular signaling from cell-surface receptors for multiple cytokines implicated in the pathologic processes of rheumatoid arthritis. 2 Baricitinib, an orally available small molecule, provides reversible inhibition of JAK1 and JAK2 and has shown clinical efficacy in studies . . .