The thyroid is a highly specialized endocrine organ devoted to the production of
thyroid hormone, via organification of inorganic iodine. To accomplish this task, the
thyroid follicular cell employs a rather complex of unique enzymes, transporters and
regulatory factors. Both a classical endocrine feedback mechanism and less understood
intracellular mechanisms maintain a constant output of thyroid hormone in normal
physiology. Such a complex system can be altered by a number of pharmacological
interferences. These interferences can be grouped under two broad categories: direct toxic
effects on the thyroid gland, and immune mediated effects precipitated by immune
modulators. Drug effects on the thyroid have been studied for several decades thanks to the
availability of accurate methods for assessing thyroid physiology. The effects of some of
these drugs, such as amiodarone and lithium have been known for many years, but novel
antineoplastic agents introduced more recently have been the focus of intense attention over
the past few years. This chapter concisely summarizes our current knowledge on drugs
capable of altering thyroid function or structure, with attention to underlying mechanisms.
Keywords: Alemtuzumab, amiodarone, endocrine disruption, drugs, interferon-
α, interferon-β, interlekin-2, lithium, thyroid gland, toxicity, tyrosine kinase
inhibitors.
