Box 3.27Drugs and the thyroid gland

Drugs can alter thyroid hormone status by affecting thyroid hormone synthesis, transport or metabolism. They act at a number of sites to:

  • Block I- uptake, e.g. lithium.
  • Decrease iodination of the tyrosine molecules in thyroglobulin, e.g. some sulfonamides and sulfonylureas.
  • Inhibit hormone secretion, e.g. lithium
  • Alter thyroid binding globulin concentration and, thus, concentrations of ‘free’ thyroid hormones, e.g. estrogens, clofibrate increase TBG whilst androgens, glucocorticoids and l-asparginase decrease TBG.
  • Alter binding to TBG or transthyretin, e.g. salicylates, phenytoin and some non-steroidal anti-inflammatories such as fenclofenac.
  • Decrease conversion of T4 to T3, e.g. glucocorticoids, propranolol, amiodarone, some iodinated radiographic contrast agents.
  • Increase hormone degradation or excretion, e.g. phenytoin, carbamazepine, cholestyramine.

From: Chapter 3, The thyroid gland

Cover of Endocrinology
Endocrinology: An Integrated Approach.
Nussey S, Whitehead S.
Copyright © 2001, BIOS Scientific Publishers Limited.

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