Methimazole

Also known as: Tapazole (brand), thionamide antithyroid drug, carbimazole (prodrug)

Other

In plain English

Methimazole lowers thyroid hormone production and is the main pill for an overactive thyroid (hyperthyroidism), such as Graves' disease. It is usually taken by mouth; a compounded skin (transdermal) gel exists (used more in veterinary practice) but is not a standard human route. Regular blood tests track thyroid levels, and rare but serious effects on the liver and white blood cells require prompt attention.

The science

Methimazole is a thionamide that inhibits thyroid peroxidase, blocking iodination of tyrosine residues on thyroglobulin and thus synthesis of T4 and T3 (it does not block peripheral T4-to-T3 conversion, unlike propylthiouracil). In non-pregnant adults it is preferred over propylthiouracil for once-daily dosing and lower hepatotoxicity; euthyroidism typically takes weeks, with dose titrated to free T4.

References

• Bordoni B & Varacallo M / methimazole, Methimazole, StatPearls (NCBI Bookshelf) 2023
• Pokhrel B & Bhusal K, Graves Disease, StatPearls (NCBI Bookshelf) 2023