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Upon completion of the chapter, the reader will be able to:

  1. Discuss the prevalence of common thyroid disorders, including mild and overt hypothyroidism and hyperthyroidism.

  2. Explain the major components of the hypothalamic–pituitary–thyroid axis and interaction among these components.

  3. Discuss the relationship between serum thyroid-stimulating hormone (TSH) levels and primary thyroid disease, and advantages for the use of TSH levels over other tests such as serum T4 (thyroxine) and T3 (triiodothyronine) levels.

  4. Identify typical signs and symptoms of hypothyroidism and consequences of suboptimal treatment.

  5. Describe clinical use of levothyroxine (LT4) in the treatment of hypothyroidism.

  6. Discuss issues regarding LT4 product bioequivalence and reasons for maintaining patients on the same product.

  7. Describe the management of hypothyroidism and hyperthyroidism in special populations, including pregnant women.

  8. Identify typical signs and symptoms of Graves disease and consequences of inadequate treatment.

  9. Discuss the pharmacotherapy of Graves disease, including advantages and disadvantages of antithyroid drugs versus radioactive iodine, adverse effects, and patient monitoring.

  10. Describe potential effects of selected drugs including amiodarone, lithium, interferon-α, tyrosine kinase inhibitors (TKIs), and immune checkpoint inhibitors on thyroid function.


Thyroid disorders are common, with more than 2 billion people or 38% of the world’s population having iodine deficiency, resulting in 74 million people with goiter. Although overt iodine deficiency is not a significant problem in developed countries, a number of common thyroid conditions exist. The most common are hypothyroidism and hyperthyroidism, which often require long-term pharmacotherapy. Undetected or improperly treated thyroid disease can result in long-term adverse sequelae, including increased mortality. It is important that clinicians are aware of the prevalence of thyroid disorders, methods of identifying thyroid disorders, and appropriate therapy. This chapter focuses on the most common pharmacologically treated thyroid disorders.


In iodine sufficient countries such as the United States, United Kingdom, and other Western European countries, overall prevalence of hypothyroidism ranges from 1% to 2%. More specifically, in the United States, overall prevalence of overt hypothyroidism ranges from 0.3% to 3.7% in various studies, depending on how hypothyroidism is defined and patient population studied. Prevalence increases with age, rising to 7% in people between 85 and 89 years.1 Compared with the total population, people aged 50 to 79 years have an almost twofold higher prevalence, and those aged 80 years and older have a fivefold higher prevalence. Prevalence of hypothyroidism is similar in White and Hispanic patients but lower in those of African or Afro-Caribbean descent. Pregnant women have a higher prevalence of hypothyroidism than nonpregnant women across all races and ethnicities.

Prevalence of overt hyperthyroidism ranges from 0.2% to 1.3% in iodine-sufficient parts of the world. In the United States, overt hyperthyroidism was detected in 0.5% of the general population, while 0.7% had subclinical hyperthyroidism. The Colorado Thyroid Health Survey assessed thyroid function in 25,862 subjects attending a ...

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