Desiccated thyroid extract, made from dried animal glands, was the most common form of treatment for hypothyroidism (low thyroid hormone levels) before the individual thyroid hormones (T3 and T4) were discovered and became commercially available. During the 1960s, science-based physicians stopped using it because its potency can vary from batch to batch, which would make it harder to optimize the patient’s thyroid hormone levels. The most commonly used brand of desiccated thyroid is Armour Thyroid®, which is made from pig thyroid glands by Forest Pharmaceuticals, Inc., a subsidiary of Forest Laboratories, Inc., of St. Louis.
Forest’s Web site displays the slogan “achieve normal thyroid levels—naturally” throughout its Web site. However, the American Thyroid Association (ATA) points out:
While desiccated thyroid contains both T4 and T3, the balance of T4 and T3 in animals is not the same as in humans, so the hormones in animal thyroid pills aren’t necessarily “natural” for the human body. Further, the amounts of both T4 and T3 can vary in every batch of desiccated thyroid, making it harder to keep blood levels right. Finally, even desiccated thyroid pills have chemicals (binders) in them to hold the pill together, so they are not completely “natural”. Desiccated animal thyroid is rarely prescribed today, and there is no evidence that desiccated thyroid has any advantage over synthetic T4 .
The ATA’s clinical guidelines, cosponsored by the American Society of Endocrinologists (AACE), also warn that desiccated thyroid should not be used to treat women with hypothyroidism who are pregnant or trying to conceive because lowering of T4 (as might occur with desiccated thyroid) may cause subnormal intellectual levels in theit offspring [2}.
The British Thyroid Association (BTA) also advises against the use of desiccated thyroid:
Armour Thyroid (USP) and Combined Thyroxine/ Tri-iodothyronine
Doctors who prescribe desiccated thyroid typically diagnose “hypothyroidism” (underactive thyroid gland) in people with normal thyroid function. Many of these doctor base their diagnosis on “low” temperature readings determined by placing the thermometer under the armpit. This is not a valid test of thyroid function. Proper diagnosis requires blood tests that measure thyroid hormone levels. The Forest Pharmaceuticals Web site has a “Physician Locator” database that contains about 960 names.
Because synthetic hormones are more reliable, the prescription of desiccated thyroid should be considered a sign of poor medical judgment. Even worse, from what I have seen, many doctors who prescribe it are prone to misdiagnose and overtreat patients in other ways. My advice is very simple: If you encounter anyone who routinely prescribes desiccated thyroid extract, head for the nearest exit.
- Regulatory Actions Related to the Use of Desiccated Thyroid
- ATA/AACE Clinical Guidelines for Treating Hypothyroidism in Adults
- FAQ: Thyroid treatment. American Thyroid Association. Web site, June 6, 2012.
- Garber JR and others. Clinical practice guidelines for hypothyroidism in adults. Endocrine Practice 10:969-1028, 2012.
- An FDA enforcement removed more than half a million bottles of Armour Thyroid from US pharmacies in 2005 due to unstable concentrations of thyroid hormone in the preparation.
- Bunevicius R, Kazanavicius G, Zalinkevicius R, Prange AJ Jr. Effects of thyroxine as compared with thyroxine plus triiodothyronine in patients with hypothyroidism. N Engl J Med. 1999; 340: 424-9.
- Escobar-Morreale HF, Botella-Carretero JI, Escobar del Rey F, Morreale de Escobar G. Review: Treatment of hypothyroidism with combinations of levothyroxine plus liothyronine. J Clin Endocrinol Metab. 2005; 90: 4946-54.
- Grozinsky-Glasberg S, Fraser A, Nahshoni E, Weizman A, Leibovici L. Thyroxine-triiodothyronine combination therapy versus thyroxine monotherapy for clinical hypothyroidism: meta-analysis of randomized controlled trials. J Clin Endocrinol Metab 2006; 91: 2592-9.
This article was revised on September 10, 2013.