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Myths and Controversies: Natural Desiccated Thyroid

If you've asked your doctor to prescribe natural desiccated thyroid (NDT), you may have gotten -- or may get --  pushback. That's because among many endocrinologists and conventional physicians, NDT is considered controversial. Some doctors are misinformed about NDT. And, some doctors refuse to even discuss NDT or prescribe it, or only prescribe it reluctantly.

What's going on? NDT was safely and effectively used for more than half a century, and it's again regaining popularity. But here are some of the issues myths, misinformation, and controversies surrounding NDT you might encounter.


"NDT is too old fashioned"

Many practitioners dismiss natural desiccated thyroid and "too old-fashioned." The reality is that NDT was the first – and only – treatment for hypothyroidism from the late 1800s until the 1950s. NDT drugs have been safely used as an effective hypothyroidism treatment for more than 100 years. Like NDT, other "old-fashioned drugs" like aspirin (1890s) and penicillin (1920s) are also still in widespread use, alongside newer medications. 



“There’s no difference, so you should just take levothyroxine”

Some doctors say that all thyroid hormone replacement is the same, so you might as well take levothyroxine. 

The truth is that NDT and levothyroxine are very different. 

NDT is derived from the dried thyroid glands of pigs, and has T4, T3, and other cofactors like T1, T2, and calcitonin. Levothyroxine is a synthetic version of just the T4 hormone. Levothyroxine treatment relies on the belief -- proven wrong -- that everyone can convert T4 into T3 effectively, and in needed amounts to resolve hypothyroidism. 



Some practitioners claim that levothyroxine is more effective than NDT, and that it is better at controlling hypothyroidism and thyroid test levels. 

Recent studies, however, show that a significant percentage of hypothyroid patients taking levothyroxine actually have abnormal test levels and continued symptoms. Interestingly, numerous studies also show that a majority of patients prefer NDT over levothyroxine


“Levothyroxine controls thyroid levels better than NDT" and "Levothyroxine is more effective than NDT”


“NDT is not FDA-approved”

NDT was in use long before the US Food and Drug Administration (FDA) was created.  As a result, NDT was among a number of necessary drugs that were "grandfathered" in and not required to go through what's called the new drug application (NDA) process for FDA approval. It was and continues to be legal to prescribe NDT for hypothyroidism. 

​When levothyroxine was first introduced, it was also grandfathered by the FDA, because the manufacturers claimed it was similar to NDT. Between 1990 and 1997, there were 10 levothyroxine recalls, affecting 100 million tablets, made by 37 different manufacturers and repackagers of levothyroxine. The FDA identified widespread and ongoing problems with content uniformity, sub-potency, and stability failures in levothyroxine drugs.

​As a result, the FDA undertook an effort to standardize levothyroxine tablets and reduce the instances of potency problems. In August of 1997, the FDA declared levothyroxine sodium tablets a “new drug.” Going forward, anyone who wanted to continue marketing levothyroxine needed to submit a New Drug Application (NDA), or file a petition describing why an NDA was not necessary.


​Between June 1999 and July 2001, several companies submitted NDAs, and the first product (Unithroid) was approved in August of 2000. Synthroid's petition to bypass the NDA process was rejected by the FDA, and an NDA was ultimately filed for Synthroid, which was eventually approved. Currently, a number of FDA-approved brand-name levothyroxine drugs and generic equivalents are available in the United States. 


​So, while NDT is not "FDA-approved," it is FDA-regulated. And, because NDT is an FDA-regulated drug, manufacturers must adhere to FDA guidelines that standardize natural desiccated thyroid production, and meet potency and consistency standards or face FDA recall.


“NDT is not consistent!”

Decades ago, the potency and consistency of NDT was standardized based on its iodine content. This resulted in some issues with potency fluctuations. Unfortunately, some practitioners wrongly believe these same concerns still apply, years after changes.


The reality? NDT manufacturers must follow FDA guidelines on “Good Manufacturing Practice” and these drugs are standardized based on the T4 and T3 content.


​Specifically, a 1 grain (60 or 65 mg) tablet needs to contain 38 mcg T4 and 9 mcg T3 with a margin of error of plus or minus 10%. The measured amount of T4 and T3 in NDT tablets must, therefore, be between 34.2 and 41.8 mcg of T4 and 8.1 to 9.9 mcg of T3.


Manufacturers are required to ensure that their medications meet those standards throughout each lot's expiration date.


“You don’t need T3!”

Many conventional physicians and endocrinologists believe that treatment with T3 – the active thyroid hormone -- is rarely necessary, and that T4 treatment (levothyroxine) is sufficient. Their rationale is that for someone with a normal thyroid gland, most of the daily required amount of T3 is not produced by the thyroid itself. Instead it is produced when the T4 hormone is converted into T3 by “deiodination” – also known as T4 to T3 conversion. In this process, the T4 hormone loses an iodine molecule to become T3.

​The typical daily T3 requirement in a 154 pound (70 kg) healthy adult is around 30 mcg. The thyroid gland itself produces around 5 mcg of that T3. The remaining 25 mcg of T3 is produced by T4 to T3 conversion. It’s thought then, that by taking an adequate dosage of levothyroxine, enough of that T4 will convert to T3 to meet daily needs.​


Experts are now beginning to understand, however, that this is not the case for everyone. Some cutting-edge researchers have identified genetic defects – known as “polymorphisms” -- that make T4 to T3 conversion less effective in some people. Specifically, Antonio Bianco, MD, PhD – director of Bianco Lab at the University of Chicago, has conducted groundbreaking research on the issue, and concluded that as many as 15% of people with hypothyroidism may have these genetic defects, which cause them to need treatment with T3 in order to achieve healthy thyroid hormone levels and relieve hypothyroidism symptoms.


“It's dangerous! T3 levels are too high on NDT!”

As discussed, T3 levels peak within 2 to 6 hours after taking NDT. That means that those patients tend to have higher T3 levels than those taking levothyroxine. Some experts have concerns regarding the stimulatory effects of those higher T3 levels on the heart, including the risk of atrial fibrillation. There are also concerns regarding T3's impact on bone density and the potential to increase the risk of fractures.


Specifically, the professional associations, medical societies, and government agencies also designate natural desiccated thyroid as “high risk” for people age 65 and older due to concerns about the risk of heart rhythm abnormalities in people with underlying heart problems.


​Interestingly, various studies have found that at appropriate doses, NDT normalizes thyroid levels and eliminates the signs and symptoms of hypothyroidism as well as levothyroxine, with no adverse side effects, including heart-related symptoms. There is currently no evidence that fluctuations in T3 within the normal reference range, with normal TSH levels, constitute a risk factor.


“T3/T4 ratios are too high on NDT!”

When it comes to T3 and T4 levels:

  • Patients who take NDT typically have a much higher T3/T4 ratio

  • Patients who take NDT have T3 levels that peak between two to six hours after taking their medication. The peak depends on the dose taken, but can go as high as 40 to 80% above baseline T3 levels, and continue for several hours


Some doctors point to the T3/T4 ratio, and higher peak T3 levels, as reasons not to prescribe NDT. This is not a scientifically supported conclusion, however. The data from all published clinical trials (studying around 1000 patients for up to a year), and an observational study of 400 patients over nine years, do not show increased risk or health complications in patients taking NDT, compared to levothyroxine.


“I only prescribe levothyroxine!” 

Because levothyroxine replaced NDT in the 1960s as the preferred thyroid treatment, there are now several generations of physicians who have limited training, a poor understanding of, and minimal clinical experience prescribing NDT. As a result, they also have little experience managing patients on NDT drugs.

Many of these practitioners simply avoid prescribing NDT rather than learning how to correctly prescribe and treat patients with NDT.



"Levothyroxine is the only 'accepted' treatment" and “My medical society doesn’t support the use of NDT”

All the professional thyroid associations and medical societies in the U.S. – including the American Thyroid Association and the American Association of Clinical Endocrinologists – have issued guidelines stating that patients should initially be treated only with levothyroxine. Only when those patients clearly have not benefited should a T4/T3 treatment be tried. Even then, the societies typically recommend combination therapy of levothyroxine with synthetic T3 (liothyronine), rather than NDT. 

Research shows that NDT is an effective and safe treatment option for most patients with hypothyroidism. It should be noted that some of the largest levothyroxine manufacturers are providing financial support to these associations and medical societies and their physician members. 


“You’ll get mad cow disease!”

Here's a ridiculous claim made by some doctors. They have stated publicly that “NDT is made from cows, and can cause mad cow disease.” This is total misinformation. All NDT drugs in the U.S. are porcine (from pigs). And no cases of "mad cow disease" have been associated with NDT drugs.  



“NDT is not a prescription drug”

Some truly uninformed practitioners claim that NDT is an over-the-counter supplement that doesn't require a prescription. This is incorrect. NDT medications require a doctor's prescription, and NDT is NOT an over-the-counter supplement.

(This misinformation was even actively promoted in the past by the Ralph Nader-founded group Public Citizen's "Worst Pills, Best Pills" newsletter, which condemned NDT, claiming it was a supplement!) 


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