Peficitinib (PEF) 100 and 150 mg demonstrated robust clinical and structural efficacy in patients with RA who have an inadequate response to MTX. In Japan, two JAK inhibitors, TOF and BARI are currently available for RA patients with an inadequate response to conventional therapies. This randomized phase 3 study (RAJ4), assessed the efficacy and safety of two PEF doses in combination with MTX compared to PBO, in Japanese MTX-IR. Patients were randomized 1:1:1 to PBO, PEF 100 mg and 150 mg with M...