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Desiccated thyroid: FDA says it is a biological product, not eligible for 503A/503B compounding

Desiccatedthyroid

No. In its letter dated August 6, 2025, FDA states that animal-derived thyroid (ADT) products, sometimes described as desiccated thyroid extract, require an approved biologics license application (BLA) under section 351 of the Public Health Service Act, and that biological products subject to section 351 licensure are not eligible for the 503A and 503B compounding exemptions. This page is a regulatory explainer only. Desiccated thyroid is not available to order through AffinityRx. Compounded synthetic liothyronine (T3) and levothyroxine (T4) are a separate matter and are covered on their own page.

Not orderable on AffinityRx. Desiccated thyroid is not orderable on AffinityRx. FDA's August 6, 2025 letter says ADT products prepared by a licensed pharmacist in a state-licensed pharmacy or by an outsourcing facility are unapproved biological products. Synthetic T3 and T4 are not affected; see the compounded liothyronine / levothyroxine page.

0
FDA-approved products
none identified
Oct 2026
Status checked
FDA and state sources

By Tim Yoon, CEO, AffinityRx · Last updated

What clinics should know about Desiccated thyroid (animal-derived thyroid)

This page is a regulatory explainer. The points below are not sourcing guidance for an orderable product.

  • FDA's August 6, 2025 letter says compounded or pharmacy-prepared ADT is an unapproved biological product and is not eligible for 503A or 503B. A pharmacy that offers compounded desiccated thyroid is relying on an exemption FDA says does not apply.
  • The letter says FDA intends to take action against marketed unapproved ADT products, after a transition period of up to 12 months described in the letter, and that it will continue to apply a risk-based enforcement policy in the meantime. Check fda.gov for current status.
  • FDA identifies approved synthetic thyroid hormone replacement products (levothyroxine and liothyronine) as the alternative, and says patients should work with their healthcare providers to transition to an FDA-approved product. Prescribers decide treatment; AffinityRx does not.
  • Compounded synthetic liothyronine (T3) and levothyroxine (T4) are different: they are components of FDA-approved drugs with USP-NF monographs and may be compounded by 503A pharmacies on patient-specific prescriptions, subject to the essentially-a-copy conditions. Confirm the SKU names synthetic T3 or T4, not desiccated or porcine thyroid.
  • AffinityRx does not offer desiccated thyroid, and this page is a regulatory explainer, not an availability page.

Desiccated thyroid (animal-derived thyroid) compounding regulatory status (2026)

FDA considers animal-derived thyroid (ADT), also called desiccated thyroid, to be a biological product, so compounded desiccated thyroid is not eligible for the 503A or 503B compounding exemptions.

In its letter dated August 6, 2025, FDA states that "ADT products require an approved biologics license application (BLA) under section 351 of the Public Health Service (PHS) Act in order to be legally marketed in the U.S." and that "There are no FDA-approved BLAs for the ADT products currently on the market." The letter adds: "ADT products marketed without a biologics license under the PHS Act are unapproved biological products. This includes ADT products that are prepared by a licensed pharmacist in a state-licensed pharmacy or a federal facility, a licensed physician, or an outsourcing facility. Biological products subject to licensure under section 351 of the PHS Act are not eligible for the exemptions for compounded drugs under sections 503A and 503B of the FD&C Act." A USP Thyroid monograph does not change this. On enforcement timing, the letter states: "We believe it will require up to 12 months to safely transition patients to an FDA-approved thyroid hormone replacement product. FDA intends to provide adequate time to transition patients to an FDA-approved thyroid hormone replacement product before initiating action against manufacturers, distributors, and importers of ADT and unapproved ADT products intended for commercial distribution. During this time, FDA will continue to apply a risk-based enforcement policy." The letter gives no calendar end date for that period. This does not affect synthetic liothyronine (T3) and levothyroxine (T4), which are components of FDA-approved drugs with USP-NF monographs; see the compounded liothyronine / levothyroxine page.

AffinityRx found no FDA-approved drug product with Desiccated thyroid (animal-derived thyroid) as its active ingredient.

Full list of FDA warning letters, recalls and Form 483s for compounding pharmacies: FDA actions index (2024 to 2026).

Frequently asked questions about compounded Desiccated thyroid (animal-derived thyroid)

Can pharmacies compound desiccated thyroid?
No, according to FDA. In its August 6, 2025 letter, FDA states that biological products subject to section 351 licensure are not eligible for the exemptions for compounded drugs under sections 503A and 503B, and that this includes ADT products prepared by a licensed pharmacist in a state-licensed pharmacy or by an outsourcing facility. The existence of a USP Thyroid monograph does not create a compounding exemption.
Why does FDA treat desiccated thyroid as a biological product?
FDA's letter says ADT is derived from animal thyroid glands and necessarily contains thyroglobulin, a protein of 2,770 amino acids, so it meets the definition of a biological product in section 351(i)(1) of the PHS Act. The letter states that ADT products require an approved BLA, and that there are no FDA-approved BLAs for the ADT products currently on the market.
What did FDA say about enforcement timing?
The letter states: "We believe it will require up to 12 months to safely transition patients to an FDA-approved thyroid hormone replacement product. FDA intends to provide adequate time to transition patients ... before initiating action against manufacturers, distributors, and importers of ADT and unapproved ADT products intended for commercial distribution. During this time, FDA will continue to apply a risk-based enforcement policy." The letter does not give a calendar end date. Check fda.gov for current status.
Is desiccated thyroid FDA-approved?
No. FDA's August 6, 2025 letter says there are no FDA-approved BLAs for the ADT products currently on the market, so products such as Armour Thyroid and NP Thyroid are unapproved. FDA-approved thyroid hormone replacement products are synthetic levothyroxine and synthetic liothyronine.
Can clinics order desiccated thyroid through AffinityRx?
No. AffinityRx does not offer desiccated (animal-derived) thyroid, and this page is a regulatory explainer only. AffinityRx is not a pharmacy.
Is compounded T3 (liothyronine) or levothyroxine (T4) affected?
No. FDA's letter concerns animal-derived thyroid. Synthetic liothyronine and levothyroxine are components of FDA-approved drugs with USP-NF monographs, and state-licensed 503A pharmacies may compound them on patient-specific prescriptions, subject to the essentially-a-copy conditions of section 503A(b)(1)(D). See the compounded liothyronine / levothyroxine page.
Is thyroid hormone a controlled substance?
No, thyroid hormones are not controlled substances, so no DEA registration is required. That is separate from the biological product issue FDA raised for ADT.

Sources

Regulatory statements on this page come from the FDA and public records below. Verify current status on fda.gov before relying on it.

  1. https://www.fda.gov/media/188081/download
  2. https://www.fda.gov/drugs/human-drug-compounding/bulk-drug-substances-used-compounding-under-section-503a-fdc-act
  3. https://www.accessdata.fda.gov/scripts/cder/daf/

By Tim Yoon, CEO, AffinityRx · Last updated

Questions about thyroid medication sourcing?

AffinityRx does not offer animal-derived thyroid. Ask about synthetic liothyronine and levothyroxine, which are covered on their own page.

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