Okay, kids, grab your history books! A long, long time ago, if you had an underactive thyroid, it was bad news. There was no treatment for your condition, and you could eventually die. Then, in the 1880s, a doctor started experimenting with an extract of animal thyroid glands to treat hypothyroidism.
Newsflash: it worked! With that discovery, hypothyroidism was no longer an untreatable and fatal condition. By the 1930s, the first commercially manufactured thyroid drug – naturally desiccated thyroid (NDT) – became available. It was the start of a new age for thyroid treatment.
Fast-forward to 2020. NDT is still available and has been a safe and effective hypothyroidism treatment for more than a century. But for many practitioners and patients, "thyroid hormone replacement medication" is synonymous with levothyroxine – the synthetic form of one thyroid hormone, thyroxine (T4). This changed in 1970 when it was discovered that we convert T4 to T3. However, we typically do not convert T4 to T3 well when we have hypothyroidism.
For the last few decades, NDT has been a source of controversy and conflict in the thyroid community. What's going on? How could a lifesaving breakthrough medication end up with such a bad rap? Why is there such pushback against a trusted treatment for hypothyroidism?
Let's look at some of the facts and fiction about NDT.
What is Natural Desiccated Thyroid?
NDT – also referred to as desiccated thyroid extract (DTE) or "porcine thyroid" – is a thyroid hormone replacement medication that has been in continuous use since the early 1900s. It was the first treatment for hypothyroidism and the only available treatment for the first half of the twentieth century.
Levothyroxine (Synthroid, Levoxyl, Unithroid, Tirosint, etc.) is a synthetic version of just one thyroid hormone – thyroxine (T4). NDT – a natural drug made from the dried ("desiccated") thyroid glands of pigs – includes not only T4 but the active thyroid hormone, T3.
There are four brands of natural desiccated thyroid currently available in the United States by prescription, including:
The FDA also designates NP Thyroid® as a "generic" equivalent to Armour® Thyroid.
Who benefits from NDT?
NDT includes both thyroid hormones: thyroxine (T4) and triiodothyronine (T3), which means it's usually of most benefit to hypothyroid patients who need a treatment that includes T3. NDT's also contain calcitonin, T1 an T2 because they are derived from mammals. But how can you predict if you might feel better taking NDT for your hypothyroidism?
Here are a few indicators:
Keep in mind that the only way to know for sure if you will feel better on NDT is a trial of the medication. Your goal? Get to optimal TSH, Free T4, and Free T3 levels, and then see whether your symptoms respond positively to the NDT treatment over time.
The challenge of getting treated with NDT
You may find it challenging to find a doctor who will prescribe NDT. The reason? The predominance of levothyroxine treatment has left many physicians misinformed about NDT.
Here are just a few of the concerns you may hear about NDT:
"NDT is too old fashioned."
Many conventional physicians view NDT as too old-fashioned. This viewpoint is surprising, actually, given that NDT has been used safely and effectively for more than 100 years. Yet, some doctors still regularly prescribe other "old-fashioned drugs" such as aspirin and penicillin alongside newer medications.
"Levothyroxine is more effective than NDT."
Some practitioners claim that levothyroxine is a more effective treatment than NDT and better controls thyroid test levels. However, recent studies show that many patients who take levothyroxine still have abnormal test levels and continued symptoms. And research studies have shown that among patients who have taken levothyroxine and NDT, more patients prefer NDT treatment. I personally am on tirosint and T3. The big problem with synthetic t4 medications is the fillers and dyes. Also, T4 only doesn't work for most of us. We need to add a T3. Not everyone does well on NDT meds, and not everyone does well on synthetic meds. It is trial and error.
"NDT is not FDA-approved."
NDT was in use long before the U.S. Food and Drug Administration (FDA) came into existence. As a result, the FDA "grandfathered" NDT and never required a new drug application (NDA) for FDA approval. So, while NDT is not officially "FDA-approved," it is strictly regulated by the FDA, and legal to prescribe as a hypothyroidism treatment. Like any FDA-regulated drug, NDT also meets stringent FDA manufacturing guidelines for potency and consistency.
"T3 levels are too high on NDT!"
Because T3 peaks quickly in the body – usually within two to six hours – patients taking NDT have higher T3 levels and T3 to T4 ratios than patients taking levothyroxine. Some experts express concerns that the higher T3 levels are too stimulating on the heart and increase atrial fibrillation risk. There are also concerns regarding T3's potential negative impact on bone density and the risk of fractures. However, various studies have found that at appropriate doses, NDT normalizes thyroid levels and eliminates the signs and symptoms of hypothyroidism equally as well as levothyroxine, with no adverse side effects, including heart- and bone density-related symptoms. There is currently no evidence that fluctuations in T3 within the normal reference range, with normal TSH levels, constitute any excess risk.
"You'll get mad cow disease!"
This claim is one of the silliest. The fact is that all NDT drugs in the U.S. are from the thyroid glands of pigs – not cows. No cases of "mad cow disease" have ever been associated with prescription NDT drugs.
"NDT is not a prescription drug."
Finally, you may be told that NDT is an over-the-counter supplement and doesn't even require a prescription. This is not true. In this case, NDT may be confused with over-the-counter thyroid glandular supplements. All genuine NDT medications require a doctor's prescription, and NDT is not available over-the-counter as a supplement.
Finding a healthcare provider
A significant challenge many patients face is finding a health care provider willing to prescribe NDT.
If your current practitioner is resistant to discussing alternative treatments, find a more open-minded provider. In addition to endocrinologists, other types of doctors also have expertise in treating the thyroid holistically, so it's important to do your research. Your ideal provider may be a naturopathic physician (ND) or an osteopathic physician (DO). You may also find the best hypothyroidism treatment from a nurse practitioner (NP) or a physician assistant (PA).
Tips for when you start taking NDT
When you're starting or taking NDT, here are a few guidelines to keep in mind:
Also, keep in mind that because the T3 in NDT peaks rapidly in the bloodstream, some patients enjoy the best results with a split or divided dosage, taking some NDT in the morning and the rest in the afternoon.