Leminoprazole Products | Cleanchem - Leflunomide is a disease-modifying antirheumatic drug (DMARD) used to treat rheumatoid arthritis and psoriatic arthritis. It inhibits dihydroorotate dehydrogenase, a key enzyme in pyrimidine synthesis, thereby suppressing the proliferation of activated lymphocytes. Leflunomide helps reduce joint inflammation and progression of structural damage. It may cause liver toxicity, so liver function monitoring is essential.