Leflunomide is primarily used as an immunomodulatory agent in the treatment of autoimmune diseases, especially rheumatoid arthritis. It works by inhibiting pyrimidine synthesis in rapidly dividing immune cells, thereby suppressing the overactive immune response that contributes to joint inflammation and damage. Its main therapeutic benefit lies in reducing disease progression, improving physical function, and alleviating symptoms such as joint pain and swelling. Leflunomide is often prescribed when other disease-modifying antirheumatic drugs (DMARDs) have not been effective. It is also investigated for use in preventing organ transplant rejection due to its ability to modulate T-cell activity. The drug is taken orally and offers a long half-life, allowing for once-daily dosing, which supports patient compliance. Monitoring of liver function and blood counts is recommended during treatment due to potential adverse effects.