Used to treat moderate to severe rheumatoid arthritis in adults who have not responded well to other treatments. It is a Janus kinase (JAK) inhibitor that works by blocking immune signals to reduce inflammation, alleviate joint pain and swelling, and slow joint damage. Also approved for severe alopecia areata in adults and adolescents, helping regrow hair by targeting the immune attack on hair follicles. Authorized for emergency use in hospitalized adults with COVID-19 requiring oxygen, to mitigate lung inflammation and prevent acute respiratory distress. Explored for other autoimmune conditions like atopic dermatitis. Taken orally for convenience over injectables.