The treatment of rheumatoid arthritis has changed dramatically over the last two decades since the development of biological disease-modifying anti-rheumatic drugs (bDMARDs). Moreover, Janus kinase (JAK) inhibitors became available in 2013. JAK inhibitors are low-molecular-weight compounds, which exert anti-rheumatic effects by suppressing the action of JAK, an intracellular tyrosine kinase. Of note, biologics bind to extracellular proteins and block their activity. The availability of JAK inhibitors that are as effective as bDMARDs, despite the completely different route of administration and mode of action, has enabled the treatment of rheumatoid arthritis to enter a new stage. JAK inhibitors are useful in a variety of cases, including patients who inadequately responded to treatment with methotrexate and/or bDMARDs. Oral administration is convenient for patients. Nevertheless, the drugs should be carefully prescribed as they are metabolized in the liver and kidneys. Attention should also be paid to adverse events, such as infections including herpes zoster. It is necessary to understand the characteristics of JAK inhibitors and use these agents judiciously.

Keywords: JAK inhibitor; Rheumatoid arthritis; adverse event; efficacy; selectivity.