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Hypothyroidism and hyperthyroidism are relatively common endocrine disorders. The global incidence of neonatal hypothyroidism is 1 per 3000–4500 births. It is estimated that hypothyroidism affects 1%–5% of US adults. It is more prevalent in whites than people of Hispanic or African American descent. In the elderly, the prevalence of hypothyroidism increases to 15% by age 75. Worldwide, iodine deficiency is the leading cause of hypothyroidism. According to US retail pharmaceutical statistics for prescription drugs, levothyroxine (both generic and Synthroid combined) (T4) has consistently ranked in the top five for overall total prescription count, with an average 67 million per year. Many cases of intentional and unintentional overdoses with thyroid hormone are reported in both adults and children.60 Despite the profound effects of thyroid hormones on physiologic homeostasis and the widespread use and access to exogenous thyroid hormone, morbidity, and mortality from overdose is very low.

Long before the thyroid was recognized as a functional endocrine gland, it was believed to serve a cosmetic function, especially in women. Egyptian paintings often emphasize the full and beautiful necks of women with enlarged thyroid glands. Early theories on the physiologic function of the thyroid gland included lubrication of the trachea, diversion of blood flow from the brain and protection of women from "irritation" and "vexation" from men.34 Although poorly defined in historical accounts, symptoms resembling hypothyroidism and myxedema that were successfully treated with ground sheep thyroid were described 500 years ago. In the 16th century, Paracelus described the association between goiter (thyroid gland enlargement) and cretinism.64 A syndrome of cardiac hyperactivity, goiter, and exophthalmos was first described in 1786.76 Graves and von Basedow further detailed this syndrome and its relationship to the thyroid gland 50 years later.31,34,60,64,76,104

In 1891, injection of ground sheep thyroid extract was formally described as a treatment for myxedema.34 Shortly afterward, oral therapy was determined to be equally effective. Seaweed, which contains large amounts of iodine, was used to treat goiter (hypothyroidism) in Chinese medicine as early as the 3rd century A.D. In 1863, Trousseau100 fortuitously discovered a treatment for Graves disease when he inadvertently prescribed daily tincture of iodine instead of tincture of digitalis to a tachycardic, thyrotoxic young woman.

Sir Charles R. Harington described the chemical structure and performed the first synthesis of thyroxine (tetraiodothyronine [T4]) in 1926.78 Triiodothyronine (T3) was not isolated and synthesized until the 1950s.34 Prior to this, desiccated thyroid gland from animal sources was commonly used to treat hypothyroidism. Despite becoming essentially obsolete in the modern medical community, unprocessed, desiccated thyroid can be easily purchased via the Internet and in health food stores as a thyroid supplement.89 Armour, a pharmaceutical grade porcine-derived thyroid supplement, is still available by prescription. Unfortunately, the misguided use of both organic and synthetic thyroid supplements as vitality agents, stimulants, and weight-loss aids has become increasingly ...

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