• Clinical science

Antithyroid drugs


Antithyroid drugs are drugs that either decrease thyroid hormone synthesis (thionamides) or thyroid hormone release (iodides). The most important group of antithyroid drugs are thionamides, which include methimazole, carbimazole, and propylthiouracil. Thionamides decrease thyroid hormone synthesis by inhibiting thyroid peroxidase, an essential enzyme involved in multiple steps of thyroid hormone synthesis. Thionamides play a significant role in the treatment of hyperthyroidism and thyroid storm. Iodides are solutions containing potassium iodide that inhibit the release of thyroid hormones into the circulation. They are, therefore, a useful adjunct treatment in the management of thyroid storm, but their main clinical use is for the preoperative preparation of a patient with Graves' disease, because they decrease the vascularity of the thyroid gland.


Active substance Mechanism of action Onset Indications
  • Rapid onset of action (within a week)


Biosynthesis of thyroid hormones

Side effects



Complete blood counts should be monitored in patients taking antithyroid drugs because of the risk of agranulocytosis/aplastic anemia. Liver function tests should be monitored in patients taking propylthiouracil because of the risk of hepatotoxicity.


We list the most important adverse effects. The selection is not exhaustive.