Leflunomide is a medication primarily used to treat autoimmune diseases, particularly rheumatoid arthritis. It works by inhibiting the production of certain immune cells, which helps reduce inflammation and joint damage associated with these conditions. This drug is often prescribed when other treatments are ineffective or not tolerated. Patients taking leflunomide may need regular blood tests to monitor liver function and blood cell counts, as it can have side effects. It is important to follow a healthcare provider's instructions while using this medication.