About Natural Desiccated Thyroid
Natural desiccated thyroid (NDT) was the first treatment for hypothyroidism, introduced in the late 1800s. It was the only hypothyroidism for half a century, when levothyroxine was introduced. Since that time, it's still in use by millions of thyroid patients.
NDT is a prescription thyroid drug, made from the dried ("desiccated") thyroid glands of pigs. NDT is also known as "porcine thyroid," thyroid extract, and "desiccated thyroid extract," or DTE. The official designated drug name is Thyroid USP.
Unlike levothyroxine, which contains only the T4 hormone, natural desiccated thyroid provides both T4 and T3 hormones in a single tablet.
To make NDT, the animal thyroid glands are dried and processed into Thyroid USP, which is mixed with fillers, binders and dyes ingredients (called excipients). It's then formed into tablets that include standardized amounts of the two key thyroid hormones, T4 (thyroxine) and T3 (triiodothyronine). Some formulations of tablets have an added outer coating.
In the United States market, there are several brand-name natural desiccated thyroid drugs currently available: Armour® Thyroid, Nature-Throid®, WP Thyroid®, and NP Thyroid®, which is also designated by the FDA as a generic equivalent to Armour Thyroid.
The US Pharmacopeia (USP) sets manufacturing standards for medications. Per USP, 1 grain of natural desiccated thyroid is standardized at 65 mg. (Note that Nature-Throid and WP Thyroid 1 grain is 65 mg.
Armour Thyroid and NP Thyroid have a different weigh of weighing ingredients, so 1 grain is 60 mg.)
1 grain is standardized at 38 mcg of T4 and 9 mcg of T3, and each tablet must contain no less than 90% and not more than 110% of the standardized T4 and T3 content
The following chart shows the dosage sizes for the four brands of NDT on the US market: