Filgotinib, the most recent molecule in the JAKi class, was approved on 20 September 2020 in the European Union and Japan; it was developed to be an ATP-competitive, reversible, JAK1 preferential inhibitor, for the treatment of inflammatory disease such as RA and ulcerative colitis (UC) (Dhillon and Keam, 2020). Here, JAK1 is linked to rheumatoid arthritis.