Drugs and thyroid function

Testing of thyroid function is common in clinical practice. Many patients who are tested, including those who have or are receiving treatment for thyroid disease, take medications that may affect thyroid function. Therefore, the possible effect of these drugs both on the results of thyroid-function tests and on the effectiveness of treatment must always be considered in decisions regarding patient care. The pathways of thyroid hormone synthesis, secretion, transport in the circulation, and metabolism offer numerous targets for drug interaction (Figure 1 and Figure 2). Normal thyroid secretion depends on thyrotropin (TSH). Secretion of TSH is, in turn, inhibited by thyroid hormones.