Stelara, generically known as ustekinumab, is a prescription medication used in the treatment of several chronic inflammatory conditions, including moderate to severe plaque psoriasis, active psoriatic arthritis, and Crohn's disease, among others. It belongs to a class of drugs known as biologics, specifically targeting and inhibiting the activity of certain proteins in the body (interleukin-12 and interleukin-23) that play key roles in inflammation and immune response. By doing so, Stelara helps to reduce the symptoms of the diseases it treats, such as skin lesions, joint pain, and digestive issues. It is administered through subcutaneous injection or intravenous infusion, the frequency of which depends on the specific condition being treated. As with any medication, it may have side effects, and its use should be closely monitored by a healthcare professional.