Desiccated thyroid extract

Desiccated Thyroid became a commercial treatment option in 1934 with Westhroid,^[citation needed]. In the early 1960s, desiccated thyroid hormones (thyroid extract) began to be replaced by levothyroxine (synthetic T4), or by combinations of T4 and T3. Replacement occurred faster in the United Kingdom than in North America, but by the 1980s more patients were being prescribed synthetic T4 (levothyroxine) or synthetic T4/T3 combinations than desiccated thyroid extract.^{[citation needed]}

Several reasons have been identified as to why prescriptions changed from desiccated thyroid treatment.

• Although thyroid extract was useful and usually effective, some patients continued to complain of fatigue, weight gain, or other symptoms. Dosing until the 1960s was often a matter of prolonged adjustment trials.^[19]
• It was known that not all of the iodine content of thyroid extract was in the form of effective T4 and T3 and that actual content of available preparations varied more than the permitted 15%.
  JAMA revealed continued large ranges of hormone content and potency in all of the available thyroid extracts on the American market.^[24]
• By the 1960s, it was known that thyroxine was the essential hormone produced by the thyroid gland, and that most T3 was manufactured in other parts of the body by deiodination of thyroxine. It was demonstrated in hypothyroid animals and people that replacement of thyroxine alone corrected the measurable manifestations (laboratory test results) of hypothyroidism.[25] By the 1970s doctors could measure T4, T3, and TSH in human blood with approximate accuracy and confirmed that treatment with thyroxine alone could produce normal blood levels of both T4 and T3,^[26] but desiccated thyroid caused supraphysiologic levels of T3.^[27] In the majority of patients normalization of these levels eliminated all signs and symptoms of hypothyroidism.^[28]
• It was discovered that a healthy person varied the amount of T3 produced from T4 in response to changing needs and conditions^{[citation needed]} and it seemed wiser not to bypass this control system by providing larger amounts of T3 than were naturally produced each day^{[improper synthesis?]}.
• Furthermore, when T3 could be measured, it was discovered that thyroid extract and synthetic combinations of T4 and T3^{[contradictory]} produced significantly greater fluctuations of T3 throughout the day than occurred in healthy people or hypothyroid people treated with thyroxine alone.^[29]
• Endocrinologists found that treatment with thyroxine alone worked as well or better than thyroid extract for the majority of patients, although even thyroxine did not reverse all the symptoms of a minority.^[28]

Thyroid care changed in other ways as well. Accurate T4 and T3 measurements became widely used in the 1970s, and by the late 1980s, TSH measurement had become sensitive enough to detect mild degrees of hyperthyroidism and overtreatment.^{[citation needed]} Blood levels of thyroid hormones and TSH were found to be the best predictors of objective benefits from thyroid replacement^{[improper synthesis?]}: those with the most severe measurable deficiency enjoyed the most dramatic and sustained benefits.^{[citation needed]} It was also discovered that even mild hyperthyroidism as defined by a suppressed TSH level, whether due to disease or overtreatment, was associated with poorer bone density in women, and with higher rates of atrial fibrillation in elderly patients.^{[citation needed]}

Society and culture

Names

This product is sometimes referred to as thyroid USP, thyroid BP. Brands differing only in binders and fillers.^{[citation needed]}

References