Updated October 06, 2014.
In the recent publication of the Clinical Practice Guidelines for Hypothyroidism in Adults, the American Association of Clinical Endocrinologists (AACE) and the American Thyroid Association (ATA) summarized the latest conventional thinking regarding diagnosis and treatment of hypothyroidism. I wrote a summary of the guidelines earlier in the month, along with an analysis of some of the most controversial hypothyroidism recommendations of the task force.
But one thing about these Guidelines is puzzling and warrants further discussion: the issue of natural desiccated thyroid drugs.

Natural desiccated thyroid -- or NDT -- is the term used to describe prescription thyroid medications that are made from the dried thyroid glands of pigs -- known in medical terminology as desiccated porcine thyroid. In the United States, two key brands are available -- Nature-Throid (made by RLC Labs) and Armour Thyroid (made by Forest Labs.) There is also a generic version of NDT made by Acella available in the U.S.

NDT has been on the market for more than 100 years, and until the 1950s, it was the only thyroid hormone replacement medication available to treat hypothyroidism. Its use became less commonplace when the synthetic drug levothyroxine came on the market, and gained favor among endocrinologists.

In the last 15 years, however, the use of NDT drugs has been on the rise, and in recent years, it's estimated that more than two million prescriptions for NDT are being written each year in the U.S.

Some patients report that their hypothyroidism symptoms seem to resolve best when taking a natural desiccated thyroid drug, rather than synthetic medications.

The mainstream endocrinology world has, however, declared war on natural thyroid drugs as a treatment option for hypothyroid patients. Misinformation is rampant. For example, some doctors tell patients that NDT drugs are going off the market soon, or are already off the market. It's also common to hear physicians say that these drugs aren't consistent, because "every pig is different." (Seriously, they say this!)

Fear-mongering is also popular. Some practitioners wrongly tell patients that they are at immediate risk of osteoporosis, or serious heart problems, when taking NDT, despite there being no evidence to support that claim.

It's also surprising how physicians, including endocrinologists, can be willfully ignorant about something as basic as the source and nature of NDT drugs.

In the past, one popular MD who had a syndicated newspaper column insisted that "Armour thyroid is extracted from the thyroid glands of cattle." When I criticized him for this error, he issued a correction stating that natural thyroid drugs were porcine, and not bovine (from cows).

In fact, it's been many decades since prescription NDT drugs in the U.S. were made from bovine thyroid.

Then there was Sidney Wolfe, MD, whose group Public Citizen and its "Best Pills, Worst Pills newsletter" called for Armour Thyroid to be taken off the market because, as they erroneously stated, " Armour Thyroid is an unregulated, over-the-counter dietary supplement." Sorry Dr. Wolfe, but it as neither. It was a prescription medication, and one that, like all prescription medications, is regulated by the Food and Drug Administration.

Back in 2009, we had the American Thyroid Association issuing a mismash of misinformation about natural thyroid including the claim that it's "mostly" from pigs. All prescription natural desiccated thyroid drugs in the U.S. ARE in fact porcine thyroid. There is no "mostly" to it.

And now, in 2012, we have the American Association of Clinical Endocrinologists (AACE) and the American Thyroid Association (ATA) issuing what are supposed to be state-of-the-art "Clinical Practice Guidelines for Hypothyroidism in Adults," and what do they say?

...the most commonly used form of desiccated thyroid, known as Armour® Thyroid, which is of porcine origin, may be viewed as a T4 and T3 combination with a ratio of approximately four to one by weight. The content of thyroid hormone and the ratio of T4 to T3 may vary in desiccated thyroid preparations depending on the brand employed and whether it is of porcine or bovine origin.

Bovine origin? What decade are these Guidelines being published in again? How can a task force of the supposedly top endocrinologists in the nation make such a blatant error in 2012?
Note to the AACE and ATA -- all of the prescription forms of NDT available in the U.S. are in fact porcine desiccated natural thyroid. There is no prescription bovine NDT available in the US, and there hasn't been for decades.

Perhaps the most disingenuous part of the discussion on NDT is "Recommendation 22.4" of the Guidelines, which states:

There is no evidence to support using desiccated thyroid hormone in preference to L-thyroxine monotherapy in the treatment of hypothyroidism and therefore desiccated thyroid hormone should not be used for the treatment of hypothyroidism. Grade D, BEL 4.

So the task force says that NDT drugs should not be prescribed to treat hypothyroidism, because there is no evidence to support using desiccated thyroid.
But it's important to note that the way these guidelines are developed, they are graded from A to D, with BEL ratings of 1 to 4. A grade of A means that a recommendation has strong and conclusive clinical evidence. A rating of D -- which is what Recommendation 22.4 has -- means that the recommendation is not evidence based, but rather based on opinion because of a lack of conclusive clinical evidence. The BEL rating is a "best evidence" rating. 1 would include substantial conclusive evidence. The rating of 4 given to this recommendation? It means "minimum conclusive evidence."

Also take a look at the phrasing. There is "no evidence to support using desiccated thyroid hormone in preference to L-thyroxine monotherapy in the treatment of hypothyroidism and therefore desiccated thyroid hormone should not be used..."

What they fail to mention is that while there is no evidence to show preference of NDT drugs (like Armour, Nature-Throid) over levothyroxine drugs (like Synthroid, Levoxyl, Levothroid, etc.), it works the other way as well. There is no evidence to support using levothyroxine drugs in preference to NDT drugs. The studies simply aren't out there. They haven't been done. And that is why Recommendation 22.4 has a Grade D, BEL 4 rating.

It's an opinion. It's an opinion that has now been codified into official "Guidelines." It's a "recommendation" that is not based on data or evidence, it's a recommendation based solely on opinion. Whose opinions? The opinions of a task force of endocrinologists, whose organizations have received financial support from big pharmaceutical companies who manufacture levothyroxine, and who themselves have in some cases received stipends, honoraria, and other financial benefits from those same drug manufacturers.

If the endocrinology world wants to issue guidelines that eliminate an entire treatment option for millions of thyroid patients, patients deserve Grade A recommendations based on science, not sloppy Grade D recommendations based on uninformed opinions. Because if you put the potentially biased -- and often misinformed -- opinions of an endocrinology task force up against the real life evidence and personal experiences of patients and practitioners -- in the absence of actual studies and science -- common sense says that the real life experience of patients and practitioners -- whose bias is to feel well -- wins hands down.

When it comes to the recommendations regarding natural desiccated thyroid, the ATA and AACE task force needs to go back to the drawing board.