The Standard
Thyroid USP is, first, a standard. The U.S. Pharmacopeia defines medicine standards for the USA. And some countries follow USP standards, especially when there are few, if any, other standards for something.
The Products
Secondly, Thyroid USP is the substance produced that conforms to the USP standard.
And on the Thyroid UK forum, we do try to use the terms Natural Desiccated Thyroid (NDT) and Desiccated Thyroid Extract (DTE) solely for products which conform to USP. Sometimes this results in admin action to ensure consistency of information.
Products which do not claim to be Thyroid USP tend to be called "thyroid glandulars" as we don't really have any other suitable term.
The current Thyroid USP standard is not readily accessible. Which makes it difficult to say anything definitive. Some of what follows is historic and might no longer be true.
Discussion
Nothing in USP demands that the animal source is porcine. It could be bovine (cattle) or ovine (sheep). But I am not aware of ANY Thyroid USP product which isn't porcine. Though there are at least a few bovine glandular products.
The USP standard was originally devised to try to ensure consistency of the product but the chemical assay techniques were nothing like as refined and capable as those now available. The standard checked the amount of iodine which was bound - and assumed that represented thyroid hormone.
More recently it has been revised to use techniques which specifically check levothyroxine and liothyronine content much more directly.
Further, in general we rely on the manufacturer's claims. For USA products, we know the FDA is involved. Similarly the relevant agencies for Canada and any EU countries.
The current official Thyroid USP monograph is not readily accessible. The link below claims to be the version from 2007 but this cannot be verified.
http://pharmacopeia.cn/v29240/usp29nf24s0_m83400.html
If you find anything incorrect, misleading, typos, links
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