'Thyroid USP' is used as shorthand for the powder produced from animal thyroids, of standardised potency. It is the official USA specification used for desiccated thyroid powder used to manufacture desiccated thyroid products. The same term is used worldwide.
(This does NOT apply to the numerous thyroid glandular and "support" products which could contain anywhere from no iodine at all to a much greater amount than any desiccated thyroid product.)
Any product - whether synthetic or based on Thyroid USP - which contains thyroid hormone contains iodine. That is because around 65% of T4 by weight - and 57% of T3 - is iodine. Therefore a common 100 microgram levothyroxine tablet contains about 65 micrograms of iodine in the form of T4.
Any product which contains desiccated thyroid contains iodine over and above the amount in its thyroid hormone content. This is because the thyroid gland takes in iodine, stores it, and processes it, in order to function and produce thyroid hormones. And this iodine will remain in products made from Thyroid USP. Wiki correctly says:
Before modern assays, the potency [of Thyroid USP] was specified only by iodine content ("not less than 0.17% and not more than 0.23%"), rather than hormonal content or activity.
https://en.wikipedia.org/wiki/Lugol%27s_iodine
Using the mid-point of 0.20%, each grain (taken to be 60 milligrams) of a standard desiccated thyroid product based on Thyroid USP would contain around 120 micrograms of iodine (in the forms of oxidised ions of iodine, monoiodotyrosine (MIT) or diiodotyrosine (DIT), etc.), including the amount present in the thyroid hormone content.
Using standard potencies (38 micrograms of T4 and 9 micrograms of T3 per 60 milligram), around 25 micrograms of iodine is present in T4 and 5 micrograms in T3 - that is, 30 micrograms combined.
Which means that we expect around 90 micrograms to be present in other forms.
However, having changed from iodine content to thyroid hormone content for Thyroid USP assays, the iodine content could theoretically be somewhat higher or lower than the old iodine content assay would have allowed. Without access to manufacturer data, we cannot know exactly how much iodine is present and how much it varies from batch to batch and from product to product.
There is little information about how much of the extra 90 micrograms of iodine is accessible. I do not know how much is absorbed, and how much passes straight through, nor what effects these substances could have on the microbiome.
[i][b]helvella - Iodine Content of Thyroid USP Products[/b]
A short discussion about how much iodine would be expected in desiccated thyroid products.
Last updated 10/02/2025[/i]
Link to blog:
https://helvella.blogspot.com/p/helvella-iodine-content-of-thyroid-usp.html
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