S-Ruxolitinib is a selective inhibitor of Janus-associated kinases JAK1 and JAK2. It is primarily used in the treatment of myeloproliferative disorders such as myelofibrosis and polycythemia vera. By blocking JAK signaling pathways, it helps reduce spleen enlargement, alleviates symptoms like night sweats, weight loss, and itching, and improves overall quality of life in patients. It has also shown clinical benefit in treating acute and chronic graft-versus-host disease. Research is ongoing into its use in inflammatory conditions and certain autoimmune diseases due to its modulation of cytokine signaling. Additionally, it has been explored in dermatology for conditions like alopecia areata, where JAK-STAT pathway overactivity plays a role.