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Let's take a quick trip back in history to the late 1800s. It was a time when hypothyroidism was, for some patients, a fatal and untreatable condition. Those who even survived this condition lived a life of fatigue, depression, weight gain, and dulled thinking and concentration. Some were even institutionalized!
That's why it was so groundbreaking when, in 1981, Dr. George Redmayne Murray began using an extract from the thyroid glands of sheep to treat the most severe cases of hypothyroidism successfully. Dr. Murray's lifesaving discovery of a treatment for hypothyroidism eventually evolved into natural desiccated thyroid (NDT) drugs. NDT, made from the desiccated thyroid glands of pigs, is still in use today as one treatment option for hypothyroidism.
The arrival of levothyroxine
Levothyroxine came on the scene as a treatment option in the middle of the twentieth century and fundamentally changed the world of thyroid disease. This synthetic form of the thyroid hormone thyroxine (T4) was heavily marketed as the modern treatment for people with hypothyroidism, casting NDT as an old-fashioned and out-of-date medication. As a result of levothyroxine marketing, the use of NDT drugs dropped significantly.
In fact, NDT went from a peak of 16.6 million prescriptions in 1966 to only 4.5 million prescriptions in 1988, as levothyroxine became the standard of care in hypothyroidism treatment.
While levothyroxine remains the most commonly prescribed treatment for hypothyroidism, NDT usage has grown again since the late 1980s. A significant minority of patients use natural desiccated thyroid preparations. It's estimated that up to 29% of patients with hypothyroidism are currently using NDT drugs to treat their underactive thyroid.
That's why it was so groundbreaking when in 1981, Dr. George Redmayne Murray began using an extract from the thyroid glands of sheep to treat the most severe cases of hypothyroidism successfully. Dr. Murray's lifesaving discovery eventually evolved into natural desiccated thyroid (NDT) drugs. NDT, made from the desiccated thyroid glands of pigs, is still in use today as one treatment option for hypothyroidism. In the United States, the NDT brands available include NP Thyroid, Armour Thyroid and Adthyza.
Levothyroxine didn't come on the scene until the middle of the twentieth century. This synthetic form of the thyroid hormone thyroxine (T4) was touted as the modern treatment for hypothyroidism, casting NDT as old-fashioned and out-of-date. We currently have several levothyroxine brands available in the US, including Synthroid, Levoxyl, Unithroid, and Euthyrox tablets; several generic manufacturers of tablets; and Tirosint gel capsules and Tirosint-SOL oral solution.
NDT went from a peak of 16.6 million prescriptions in 1966 to only 4.5 million prescriptions in 1988, as levothyroxine became the standard, accepted treatment for an underactive thyroid. Since the late 1980s, NDT usage has grown again. According to a 2018 survey conducted by the American Thyroid Association, around 30 percent of hypothyroid patients currently take natural desiccated thyroid.
The choice between NDT and levothyroxine is, however, controversial. Some health care providers are willing to prescribe any thyroid hormone replacement drug that can safely and best resolve a patient's hypothyroidism. Others are adamant about only prescribing levothyroxine and prefer not to treat patients with NDT.
Thyroid hormone replacement medications
The thyroid hormone replacement medications currently available in the American market include:
- Levothyroxine brands: including Synthroid, Levoxyl, Unithroid, and Euthyrox tablets; many generic manufacturers of levothyroxine tablets; and Tirosint gel capsules and Tirosint-SOL, an oral solution of liquid levothyroxine.
- NDT Brands: including NP Thyroid, Armour Thyroid and Adthyza
- Liothyronine: Liothyronine is a synthetic form of the thyroid hormone triiodothyronine (T3). It is sometimes prescribed as a combination treatment along with levothyroxine or NDT to patients who benefit from additional T3 in their hypothyroidism treatment. The common brand name is Cytomel, and generic tablets are also available.
The controversy over levothyroxine vs. NDT
The choice between levothyroxine and NDT is a controversial one, stemming from the tension between patient-reported benefits of NDT, traditional medical practices that favor levothyroxine, and the need for more comprehensive research to fully understand the long-term effects and optimal use of NDT compared to levothyroxine.
Some healthcare providers are willing to prescribe any medication for thyroid hormone replacement therapy, as long as it will safely and best resolve a patient's hypothyroidism. Others are adamant about only prescribing levothyroxine and prefer not – or even refuse – to treat patients with NDT, calling it an "alternative treatment."
Ahead, a look at why some doctors don't support treatment with NDT.
The T4/T3 issue
A fundamental issue behind the controversy is in the understanding of the body’s need for T3 (triiodothyronine). It comes down to this: Your body uses two primary thyroid hormones made by your thyroid gland: T4 (thyroxine) and T3. T4 is a storage hormone whose only role is to convert into T3, which is the active thyroid hormone used by cells and tissues in your body.
The typical daily T3 requirement in a 150-pound healthy adult is around 30 mcg. A healthy thyroid gland itself produces about 5 mcg of that T3. The remaining 25 mcg of T3 needs to be made by the body’s conversion of T4 into T3. Mainstream endocrinology believes that if you take an adequate dosage of synthetic T4 (levothyroxine), enough of that T4 will convert into T3 to meet your daily needs and maintain normal thyroid levels.
Since the introduction of levothyroxine, many patients have anecdotally reported much better symptom relief and management of their hypothyroidism by taking desiccated thyroid medication instead of levothyroxine. The likely reason? NDT contains natural forms of both T4 and T3 hormones.
Experts are beginning to understand that—for reasons that include nutritional status, stress, and other hormonal imbalances—some patients don't convert T4 to T3 as well as thought. More recently, research has also shown that a subset of the population has a genetic defect that impairs the ability to convert T4 into T3. Many of these patients report far better symptom relief and quality of life when taking NDT because it includes T3 and doesn't rely solely on T4-to-T3 conversion.
Still, some doctors believe that measuring T3 levels and treating low-normal or low T3 are unnecessary or unbeneficial approaches to treating hypothyroidism. These doctors frequently prefer not to treat patients with NDT drugs.
Potency and consistency questions
Decades ago, NDT's potency and consistency were standardized based on its iodine content, not its T4 or T3 content, resulting in some potency fluctuations. At that time, NDT earned a reputation as having an unreliable potency and was considered inconsistent in its quality.
Unfortunately, some practitioners still believe that NDT isn't reliable or consistent.
However, the truth is that now NDT manufacturers must follow U.S. Food and Drug Administration (FDA) guidelines on what's known as "Good Manufacturing Practice," which standardizes NDT based on the T4 and T3 content.
Specifically, the US Pharmacopeia (USP) monograph for thyroid tablets specifies that a 1-grain (60 or 65 mg) tablet must 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 a 1-grain NDT tablet must, therefore, be between 34.2-41.8 mcg of T4 and 8.1-9.9 mcg of T3.
NDT manufacturers are also required to ensure that their medications meet those potency standards throughout each lot's expiration date.
Regulatory status and FDA approval
One reason given by some doctors for their reluctance to prescribe NDT is the fact that NDT drugs are not "FDA-approved." This statement is confusing and misleading. NDT was available by prescription long before the FDA came into existence. The FDA began requiring that drugs be approved for safety before they could be marketed with the passage of the Food, Drug, and Cosmetic Act (FD&C Act) in 1938. At that point, a number of drugs – including natural desiccated thyroid, sometimes referred to as desiccated thyroid extract – were "grandfathered in" by the FDA. As a grandfathered drug, the FDA allowed these drugs, including NDT, to be legally prescribed without going through the formal FDA approval process. To date, NDT drugs have not required formal FDA approval. They are, however, carefully regulated by the FDA. Companies manufacture NDT drugs according to FDA guidelines on Good Manufacturing Practice, and their formulations follow strict standards set by the US Pharmacopeia (USP).
Myths and misinformation about natural desiccated thyroid
You may also hear some popular—but very misinformed—statements from some practitioners. For example, some doctors have publicly stated that "NDT is made from cows, and can cause mad cow disease." The truth is that all NDT drugs in the US are porcine (from pigs). There have been no cases of "mad cow disease" associated with NDT drugs.
You may also hear some healthcare providers claim that NDT does not require a prescription, but instead, you can buy it at vitamin or health food stores. This statement is also incorrect. There are various over-the-counter thyroid glandular supplements on the market, but they are not prescription NDT drugs. All NDT medication used to treat hypothyroidism in the U.S. requires a doctor's prescription.
Patient preference
Finally, an important issue that contributes to the controversy is patient preference. Many previously symptomatic patients report feeling better on NDT compared to levothyroxine. In one study, 49% of patients preferred NDT, while only 19% preferred levothyroxine. In addition, some patients perceive NDT as a more "natural" option. Several studies have indicated that the majority of people saw improvements in their hypothyroid symptoms with NDT medication.
In addition, some symptomatic patients report significant improvement after switching from treatment with levothyroxine to desiccated thyroid hormone treatment. This has led to increased interest in desiccated thyroid hormone among patients seeking better symptom management.
Which thyroid medication is best for you?
For some patients, levothyroxine works well to resolve hypothyroidism and hypothyroid symptoms. In other cases, you may feel best with the addition of T3, whether by adding liothyronine to your levothyroxine treatment or taking an NDT drug.
Suppose you take levothyroxine and need a better resolution of your symptoms. In that case, you may want to discuss with your thyroid doctor if natural desiccated thyroid might be a good option for you.
As a thyroid patient, you're probably asking the operative question: "Which thyroid medication is best for me?" There's no definitive answer. Ultimately, the best thyroid hormone replacement regimen for you is the medication, brand, and dosage that best and safely manages your hypothyroidism and relieves your symptoms.
A note from Paloma Health
Whether levothyroxine or natural desiccated thyroid is the best choice for you, becoming a member of Paloma Health can significantly enhance your thyroid treatment journey. With a dedicated team of thyroid specialists, Paloma Health provides personalized care and customized treatment – including NDT drugs when it’s an appropriate treatment preference. Paloma’s approach considers your unique medical history and symptoms when recommending treatments for hypothyroidism
By becoming a Paloma member, you can monitor your thyroid hormone levels with easy access to thyroid testing, using the convenient Paloma home thyroid test kit. You’ll get expert guidance and medical care from top healthcare providers to fine-tune your treatment plan, prescribe thyroid medication, and ensure optimal thyroid function. You can also access Paloma’s specialized nutritional and health coaching, which is focused on supporting hypothyroid patients. By joining Paloma Health, you gain a supportive team of partners who are committed to helping you achieve and maintain good health, empowering you to live your best life.
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