(3S,4S)-Tofacitinib is primarily used in the treatment of autoimmune conditions, particularly rheumatoid arthritis, psoriatic arthritis, and ulcerative colitis. It works by inhibiting the Janus kinase (JAK) enzymes, which play a key role in the immune response and inflammation. This mechanism helps reduce symptoms such as joint pain, swelling, and stiffness in arthritis patients. Additionally, it is effective in managing moderate to severe ulcerative colitis by controlling inflammation in the gastrointestinal tract. Its application extends to other autoimmune disorders where immune system modulation is necessary. Due to its immunosuppressive properties, it is often used when other treatments have not been effective or are not suitable for the patient.