Leflunomide is used alone or in combination with other medications to treat rheumatoid arthritis (a condition in which the body attacks its own joints, causing pain, swelling, and loss of function). Leflunomide is in a class of medications called disease-modifying antirheumatic drugs (DMARDs). It works by decreasing inflammation and slowing the progress of the condition, which can help improve the physical activity of people with rheumatoid arthritis.