Drug Profile

In the first edition of Worst Pills, Best Pills, we wrote that natural or desiccated (dried) thyroid extract products, such as Armour Thyroid, should not be used except by those who have successfully taken it for years to control their symptoms of low thyroid hormone production (hypothyroidism).[1] Remarkably, Armour Thyroid remains among the Top 200 drugs in the United States with almost 2 million prescriptions dispensed in 2002 despite the fact that for decades levothyroxine has been recommended as the better product for the vast majority of patients. Yet, the number of Armour Thyroid prescriptions appears to be growing.

Advocates of natural thyroid hormone replacement therapy maintain that products like Armour Thyroid are superior not only because they are from a natural source (animal thyroid glands) but because they contain both important thyroid hormones, tetraiodothyronine (T4) and triiodothyronine (T3). However, in 1970 it was found that T4 was broken down to T3 in the body and that T4 given alone would give normal levels of both T4 and T3.[2] Three randomized controlled studies published in late 2003 failed to confirm any benefit of combined T4 and T3 treatment compared to T4 given alone.[3],[4],[5]

The Medical Letter on Drugs and Therapeutics, an independent source of drug information written for physicians and pharmacists that we frequently cite, concluded that synthetic levothyroxine is preferred over other forms of thyroid replacement drugs. This recommendation was originally made in 1977.[6]

The fifth edition of the AMA Drug Evaluations—an excellent source of drug information before the AMA (American Medical Association) became so tied to the pharmaceutical industry—again made the recommendation in 1983 that synthetic levothyroxine is the preferred thyroid hormone replacement treatment.[7]

The American Thyroid Association clearly stated in 2003 on its Web site: “[T]here is no evidence that desiccated thyroid, a biological preparation, has any advantage over synthetic thyroxine.”[8]

The United States Pharmacopoeia (USP) long ago established standards for all thyroid products from animal sources sold in the United States. Active thyroid hormones contain iodine and the USP standards allow that the uniformity of Thyroid Tablets USP, such as Armour Thyroid, is based on iodine content,[9] not on the direct measurement of the amount of T4 and T3 in the tablets. The advantage of synthetic levothyroxine (T4) over natural thyroid hormone is a predictable effect because of standard hormonal content.[10]Desiccated thyroid remains on a list of drugs that are inappropriate for use in older adults.[11]

Why, after over 25 years of advice to the contrary, is Armour Thyroid in the top 200 most frequently prescribed drugs in the United States? One explanation appears to be that thyroid replacement therapy with natural thyroid appears to have become a niche market for unscrupulous complementary and alternative medicine (CAM) practitioners, some of whom are licensed MDs. Some of these CAM practitioners are also promoting natural thyroid hormone as a part of their weight loss programs. This is a dangerous practice, but it is not new.

The U.S. Senate held hearings on the diet pill industry 36 years ago, in 1968.[12] During these hearings, the dangerous practice of “diet doctors” who prescribed thyroid hormone alone or in combination with the heart drug digitalis or amphetamines (speedlike drugs)—or all three together—came to light. In some cases, these diet doctors were selling these drugs directly to their patients.