PF-06651600 is a selective inhibitor of Janus kinase 1 (JAK1), developed primarily for the treatment of autoimmune and inflammatory conditions. It has been investigated in clinical trials for moderate to severe ulcerative colitis and Crohn’s disease, where it demonstrated potential in reducing disease activity by modulating immune signaling pathways involved in inflammation. Due to its targeted mechanism, it offers a favorable safety profile compared to broader immunosuppressants. Additionally, it has been studied in alopecia areata, showing significant hair regrowth in patients by interrupting the immune attack on hair follicles. Its oral bioavailability allows for convenient dosing, making it a promising option for chronic inflammatory disorders requiring long-term therapy.