Overdose leads to hypothyroidism with the corresponding symptoms of reduced metabolism and, through the feedback effect, to activation of the anterior pituitary lobe with subsequent goiter growth. This can be avoided by dose reduction as soon as a euthyroid metabolic condition is achieved and, if necessary, by additional administration of levothyroxine (see Dosage & Administration).
Negative consequences of accidental ingestion of high doses of thiamazole are not known.