JAK1 and rheumatoid arthritis: Baricitinib is approved for the treatment of RA, with reported preferential selectivity for JAK1 and JAK2.9 Upadacitinib and filgotinib are under investigation for the treatment of inflammatory diseases including RA; both drugs, as well as filgotinib's active metabolite, are reported to selectively inhibit JAK1.10, 11, 12