Baricitinib, an oral selective, and reversible, JAK1/JAK2 inhibitor was the first in the JAKi class to be approved to treat RA in the European Union (EU) [4] based on the demonstration of superior efficacy compared with placebo and tumour necrosis factor inhibitors (TNFis) in populations with an inadequate response (IR) to csDMARDs, including methotrexate (MTX) [5,6]. This evidence concerns the gene JAK1 and rheumatoid arthritis.