Halting IL-6 signaling via the monoclonal antibody sirukumab also reversed IL-6-mediated suppression of CYP3A, CYP2C9, and CYP2C19 activity in rheumatoid arthritis patients (Zhuang et al., 2015), suggesting that IL-6 is an important regulator of CYP enzymes. This evidence concerns the gene CYP3A4 and rheumatoid arthritis.