Natural desiccated thyroid (NDT) is the treatment that used to be given before levothyroxine came onto the market. It comes from pigs’ glands and contains both thyroxine (T4) and tri-iodothyronine (T3), although it has more T3 than the human thyroid produces.
American and Canadian brands of NDT are now available in the UK. The American brands are Armour Thyroid, NatureThroid, WP Thyroid and NP Thyroid. There is one Canadian brand, ERFA Thyroid.
Because natural desiccated thyroid has been around for so long it never needed to go through the licensing process in America – it was classed as a "grandfathered drug". It has always been approved by the Food and Drug Administration (FDA) but not licensed in the same way that many other drugs have been.
Although there is long-standing evidence that levothyroxine is equal in efficacy to NDT, and there are studies that have found some patients do better on Armour thyroid, there are many doctors who do not like the idea of prescribing NDT. Unfortunately, there are no randomised controlled trials using NDT.
Natural desiccated thyroid was included, along with liothyronine, in the NHS England guidance, “Items which should not routinely be prescribed in primary care: Guidance for CCGs”. It will therefore be very difficult to obtain an NHS prescription for NDT. If your GP is willing to prescribe this for you, it can be prescribed on a "named patient" basis. Many private doctors are willing to prescribe NDT because they have seen their patients improve on this.
NDT comes in grains. Generally, 1 grain is 60mg and contains 38mcg of T4 and 9mcg of T3. Some brands have 65mcg. Equivalence charts show that 1 grain of NDT has the approximate equivalence of taking 100mcg of levothyroxine. Ensure that you discuss dosages with your clinician.
You may be told by your clinician that the amounts of hormone in these branded products are unstable. This is incorrect. The USP of NDT has a similar rule to that of levothyroxine and liothyronine, which means that each NDT tablet must contain between 90% – 110% of the labelled amounts of T4 and T3.
We know that there is a group of people who find that they don’t become well unless they are treated with NDT so if you do not resolve all of your symptoms on levothyroxine, this may be an option for you if you can get it prescribed.
How should I take natural desiccated thyroid?
There are no available instructions in the patient information leaflets about how to take NDT. It is assumed that it should be taken on an empty stomach with water.
Food and drugs that can cause problems
The food and drugs that can cause problems when taking natural desiccated thyroid are assumed to be the same as those for taking levothyroxine.
For more support check out our online community:
T3/T4 Combination Treatment and NDT Guidelines
Thyroid hormone substitution: T4/T3 combination treatment and animal thyroid extracts (2014)
Use of LT4 and LT3 in the treatment of hypothyroidism – European Thyroid Association (2012)
Thyroxine –Triiodothyronine Combination Therapy Versus Thyroxine Monotherapy for Clinical Hypothyroidism: Meta-Analysis of Randomized Controlled Trials (2006)
Evidence-Based Use of Levothyroxine/Liothyronine Combinations in Treating Hypothyroidism:
A Consensus Document https://www.liebertpub.com/doi/pdf/10.1089/thy.2020.0720
Date updated: 03.10.23 (V1.4)
Review date: 11.04.22