Natural desiccated thyroid — abbreviated as NDT — is a prescription thyroid hormone replacement drug used to treat hypothyroidism, an underactive thyroid. NDT is sometimes referred to as natural thyroid, pig thyroid, porcine thyroid, or thyroid extract. It is available as a generic drug in the United States, and also under the brand names Armour Thyroid, Nature-throid, and WP Thyroid. NDT is derived from the desiccated (dried) thyroid gland of pigs.
NDT is considered an alternative to the more commonly prescribed drug levothyroxine, which is available as a generic drug, and under the brand names Synthroid, Levoxyl, Unithroid, and Tirosint in the U.S.
What is the difference between NDT and levothyroxine?
A normal thyroid gland produces a number of hormones, but the two key hormones manufactured by your body are thyroxine — abbreviated as T4 — and triiodothyronine — abbreviated as T3. The majority of hormone produced by a normal thyroid is T4. While some T3 is produced, your T4 is converted into T3. T4 is considered a storage hormone. T3 is the active hormone that helps facilitate delivery of oxygen and energy to your cells.
NDT was developed from the thyroid glands of cows — and switched quickly to pigs — in the early 20th century as the first drug treatment for hypothyroidism. Previously, there was no effective treatment for hypothyroidism, and those with significant hypothyroidism usually died over time. Because it is derived from an organic animal thyroid gland, NDT includes both T4 and T3, as well as other hormones and co-factors found in a thyroid gland. NDT was marketed by the Armour Meat Company — a pork processor — as Armour Thyroid. NDT was used exclusively for the first half of the 20th century, and when the Food and Drug Administration (FDA) began regulating drugs, Armour Thyroid was effectively “grandfathered in” as a regulated prescription medication. Later, other brands of natural thyroid, including Nature-throid and Westhroid (now WP Thyroid) were released.
Levothyroxine — sometimes abbreviated as l-thyroxine, or LT4 — is a synthetic version of T4. It was introduced to the market in the 1950s with claims that it was a more consistent and stable way to provide thyroid hormone replacement. This was based on the assumption that everyone is capable of effectively converting T4 into the active T3 thyroid hormone needed by the body to resolve hypothyroidism. The first brand name levothyroxine, Synthroid, was heavily marketed, and gained an increasing market share in hypothyroidism treatment from the 1950s through the end of the century. When levothyroxine was introduced, because it was, like NDT, used to treat hypothyroidism, it was also grandfathered in, and allowed to be sold as an FDA-regulated prescription drug without going through an application or approval process.
When levothyroxine was introduced, many physicians touted it as superior to NDT, and endocrinologists adopted it as the preferred hypothyroidism treatment. Most hypothyroid patients were eventually switched to levothyroxine, and newly diagnosed patients were started on levothyroxine. Prescription numbers for NDT dropped significantly during this time.
Along the way, some patients who had been switched from NDT to levothyroxine reported a worsening of their hypothyroidism symptoms, and in some cases, were switched back to NDT. Some of the more seasoned practitioners who had expertise prescribing NDT continued to make it an option for patients.
Meanwhile, medical schools did not teach about NDT as an option, and the newer generation of doctors tended to prescribe levothyroxine exclusively.
The revived interest in NDT
In the 1990s, interest again grew in NDT as a hypothyroidism treatment option. This was driven by:
- The increasing popularity of “natural” and alternative health options with consumers, and increasing numbers of holistic and integrative practitioners
- The rise of the internet, which made more hypothyroid patients aware that there was an option to levothyroxine
- Frustration in a subset of patients whose symptoms were not resolved with levothyroxine treatment
Dissatisfied patients — armed for the first time with information — began to ask their doctors for NDT, and the number of practitioners writing prescriptions for NDT — and patients taking the drug — grew.
The controversy over NDT
For the past two decades, the revival of popularity of NDT drugs has triggered a major controversy in the endocrinology world, as well as among health insurers, health maintenance organizations (HMOs), and thyroid patients.
On one side of the controversy are the conventional endocrinologists and physicians, who maintain that there is no role for NDT in treating hypothyroidism. NDT drugs are still not discussed in many medical schools, and some physicians even erroneously believe that these drugs are no longer on the market. Most health insurers, HMOs, and government-funded medical care do not reimburse or cover NDT drugs.
On the other side of the controversy are holistic and integrative practitioners, and patients. Many practitioners have observed that some of their patients can better resolve symptoms safely when taking NDT. A growing number of patients report relief of, or significant improvement in, their hypothyroidism symptoms after switching to NDT from levothyroxine.
The latest Clinical Practice Guidelines for Hypothyroidism in Adults, published by the American Association of Clinical Endocrinologists and the American Thyroid Association state that there is “no evidence to support using desiccated thyroid hormone in preference to L-thyroxine monotherapy in treating hypothyroidism, and therefore desiccated thyroid hormone should not be used for the treatment of hypothyroidism."
Studies on NDT
Very few research studies have been conducted comparing the safety and effectiveness of levothyroxine versus NDT. A number of studies have shown that there are quality-of-life improvements and better symptoms relief in patients who take a combination synthetic T4/T3 treatment, however. Experts have found that some patients have a genetic defect known as a polymorphism that makes them less able to convert T4 into T3, and therefore, they need the supplemental T3 to treat hypothyroidism.
One notable double-blind study was published in the reputable Journal of Clinical Endocrinology in 2013. Study author, Thanh D. Hoang, D.O., a staff endocrinologist of the Walter Reed National Military Medical Center in Bethesda, Md., reported his findings that showed that NDT is a safe and viable alternative to levothyroxine to treat hypothyroidism. In addition, after the study, 49 percent of patients preferred the NDT treatment, versus 19 percent who preferred levothyroxine. Dr. Hoang also reported that patients taking NDT lost around three pounds during the study period. Those patients taking levothyroxine did not lose weight.
If you want to try NDT
If you are interested in trying NDT as a treatment for your hypothyroidism, there are some important factors to keep in mind:
- Many conventional endocrinologist and physicians refuse to prescribe NDT, or manage patients taking NDT. You may need to see an integrative or holistic physician or licensed naturopath to get NDT prescribed.
- Your health insurance, HMO, or medical plan may not permit the use of NDT, and may not reimburse or cover the costs of NDT. (NDT, however, is typically inexpensive, and out-of-pocket costs approximately $30 per month.)
- When you are taking NDT, it’s important to not only have thyroid stimulating hormone (TSH) tested, but also your free triiodothyronine (free T3) level.
- If you are allergic to pork products. NDT is not a good option for you.
- Some people are sensitive to the stimulating effects of the T3 on the heart, and may have palpitations or a more rapid heart rate when starting or taking NDT. If you have these side effects, you may not be a good candidate for NDT. Some doctors consider NDT to be especially problematic if you have a history of heart disease, or are over the age of 70.
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Mary Shomon is a thyroid disease, hormonal and autoimmune health writer, and patient advocate. For two decades, Mary has been a leading force advocating for more effective, patient-centered thyroid and hormonal health care. Mary is the New York Times bestselling author of “The Thyroid Diet Revolution,” “Your Healthy Pregnancy with Thyroid Disease,” “Living Well With Hypothyroidism,” and 10 other books on thyroid disease and integrative health. She co-stars in two PBS health specials, “Healthy Hormones,” and “Vibrant for Life.” Follow her on Twitter at @thyroidmary or at her Facebook communities: ThyroidSupport and ThyroidDiet.