Lefno 20 Tablet contains Leflunomide 20 mg, an immunomodulatory agent primarily indicated for the treatment of active rheumatoid arthritis and psoriatic arthritis. Leflunomide acts by inhibiting dihydroorotate dehydrogenase, a key mitochondrial enzyme involved in pyrimidine synthesis, thereby reducing the proliferation of activated lymphocytes responsible for the inflammatory process. This mechanism helps in decreasing joint inflammation, pain, and structural damage associated with autoimmune arthritis. Lefno 20 is typically prescribed as part of a disease-modifying antirheumatic drug (DMARD) regimen to slow disease progression and improve physical function. It is administered orally, with dosage adjustments based on clinical response and tolerability. Common adverse effects include gastrointestinal disturbances, elevated liver enzymes, alopecia, and potential hematologic abnormalities; therefore, regular monitoring of liver function tests, complete blood counts, and renal parameters is recommended during therapy. Lefno 20 is contraindicated in pregnancy due to teratogenicity and should be used cautiously in patients with pre-existing liver disease or immunodeficiency. Patients should be advised on potential drug interactions and the importance of adherence to prescribed monitoring protocols to ensure optimal therapeutic outcomes and minimize risks.