Leflunomide is primarily used in the treatment of rheumatoid arthritis, helping to reduce inflammation and slow down joint damage. It works by inhibiting the immune system's overactive response, which is a key factor in the progression of the disease. Additionally, it is sometimes prescribed for psoriatic arthritis to manage symptoms and improve joint function. In some cases, leflunomide is also used off-label to treat other autoimmune conditions, such as lupus or certain types of vasculitis, where immune system modulation is necessary. It is often considered when other treatments, like methotrexate, are not effective or well-tolerated. Regular monitoring of liver function and blood counts is essential during its use due to potential side effects.