Stelara is a prescription medication used to treat adults with psoriasis. It is also approved to treat moderatetosevere psoriatic arthritis. Stelara belongs to a group of drugs known as monoclonal antibodies. It works by binding to specific proteins of the body that are involved in inflammation and immune response, thereby preventing these proteins from binding to other cells and causing the symptoms of psoriasis.This medication comes in an injectable form to be given just under the skin by a healthcare provider. Common side effects include upper respiratory tract infections, headache, and tiredness.