Ustekinumab is primarily used in the treatment of several autoimmune conditions. It is effective in managing moderate to severe plaque psoriasis by targeting specific proteins in the immune system that contribute to the overproduction of skin cells. Additionally, it is used for treating psoriatic arthritis, helping to reduce joint inflammation and pain while preventing further joint damage. Ustekinumab is also approved for Crohn's disease, particularly in cases where other treatments have failed, as it helps to control inflammation in the digestive tract. Furthermore, it is utilized in ulcerative colitis to induce and maintain remission by modulating the immune response. Its targeted mechanism makes it a valuable option for patients with these chronic conditions, improving quality of life and reducing symptoms.