Anti-thyroid drugs are a type of drugs used to control thyrotoxicosis. Thioamides work by inhibiting the enzyme thyroid peroxidase in the blood, and so the synthesis of thyroxine and triiodothyronine is then reduced. This blocks the uptake of iodotyrosines from the colloid.

Common adverse effects include dermatitis, urticaria, skin eruptions and arthralgia. Due to the ability of thioamides to cross the placental barrier, caution is advised for use during pregnancy.