Baricitinib, an oral selective inhibitor of JAK1 and JAK2, has proven its safety and efficacy in RA patients naïve to csDMARD therapy with no prior bDMARD [83] with inadequate response to methotrexate [84, 85] and conventional DMARD [86] and patients with an inadequate response to or side effects associated with the treatment with one or more tumor necrosis factor inhibitors and/or the other biologic DMARDs [87]. Here, JAK1 is linked to rheumatoid arthritis.