A patient with papillary or follicular thyroid carcinoma and unfavorable prognostic factors should have low serum TSH level in order to diminish the risk of recurrence. However, in order to prevent side effects on target organs (heart, bones), the levels of thyroid hormones should be inside the normal reference range. Whenever the thyroid doesn\u27t produce enough hormones in a patient with a benign thyroid disease, the patient should be treated with a hormone replacement therapy. The aim of the substitution therapy is that TSH, free T4 and free T3 are inside the normal reference ranges. Bioequivalence of different generic drugs with thyroxin may differ from 12.5 to 25%. Therefore, if one thyroxine drug is changed with another one, a laboratory test of TSH level has to be performed after six weeks
