methimazole

A thioamide inhibitor of the enzyme thyroid peroxidase (TPO), with antithyroid activity. Upon administration, methimazole inhibits the metabolism of iodide and the iodination of tyrosine residues in the thyroid hormone precursor thyroglobulin by TPO; this prevents the synthesis of the thyroid hormones triiodothyronine (T3) and thyroxine (T4).