Leflunomide is a medication used in the treatment of rheumatoid arthritis. However, during its production, impurities may be formed. These impurities can affect the quality and safety of the medication. Therefore, it is essential to monitor and control the levels of impurities in Leflunomide to ensure its efficacy and safety for patients. The most commonly reported impurities in Leflunomide include related substances, degradation products, and residual solvents.