Baricitinib, sold under the brand name Olumiant among others, is a drug for the treatment of rheumatoid arthritis (RA) in adults whose disease was not well controlled by tumor necrosis factor (TNF) inhibitors. It acts as an inhibitor of janus kinase (JAK), blocking the subtypes JAK1 and JAK2. The drug is approved for medical use in the European Union and in the United States.An important side effect of JAK inhibitors is serious bacterial, mycobacterial, fungal and viral infections.