Methimazole (MMI) and propylthiouracil (PTU) are the main antithyroid drugs used for hyperthyroidism. They inhibit the synthesis of thyroid hormone at various levels and are used as the primary treatment for hyperthyroidism or as a preparation before radioiodine therapy or thyroidectomy. MMI is the drug of choice because of its widespread availability, longer half-life and small number of severe side effects. Drugs of second choice are potassium perchlorate, beta blockers, iodine, lithium carbonate and glucocorticoids. Rituximab, a monoclonal antibody directed against human CD20, was recently proposed as a biological therapy for cases of Graves' disease unresponsive to traditional drugs.