(3R,4S)-Tofacitinib is a Janus kinase (JAK) inhibitor primarily used in the treatment of autoimmune conditions. It is approved for rheumatoid arthritis (RA), where it reduces inflammation and slows joint damage progression. It is also effective for psoriatic arthritis (PsA), alleviating symptoms like swelling, stiffness, and pain in skin and joints. Additionally, it treats ankylosing spondylitis (AS) by modulating immune responses to improve spinal mobility and reduce pain. For ulcerative colitis (UC), it induces and maintains remission. Off-label uses may include other autoimmune disorders where traditional therapies fail, targeting specific immune pathways for moderate to severe cases.