Iodine Interactions

Methimazole blocks new thyroid hormone synthesis but does not prevent the gland from using iodide already inside it. Adding a large iodine load (kelp, iodine drops, iodine-containing contrast, amiodarone) can fuel hormone production, blunt methimazole's effect, and in some cases precipitate worsening hyperthyroidism or thyroid storm.

Iodine is the raw material for thyroid hormones T4 and T3, but selenium is required to build the deiodinase enzymes that convert inactive T4 into active T3 in peripheral tissues. Selenium also powers glutathione peroxidase, which protects thyroid follicular cells from the oxidative damage of iodine handling.