Hypothyroidism
Lauren Howell, PharmD
On August 7, 2025, FDA issued a statement expressing concerns with the safety and effectiveness of unapproved, animal-derived thyroid medications. Although they are not FDA approved, outpatient community pharmacies in the United States dispensed animal-derived thyroid medications to an estimated 1.5 million patients in 2024.
“Guidance from medical societies recommends synthetic formulations of levothyroxine to minimize inconsistencies in levels of thyroid hormone that can occur with the natural product, which may result in variable clinical effects,” said Mary Bridgeman, PharmD, an internal medicine pharmacist at Robert Wood Johnson University Hospital in New Brunswick, NJ.
Two types of prescription thyroid hormone replacement medications are currently on the market. Synthetic, or laboratory made, only contain levothyroxine, liothyronine, or a combination of the two. They are the most commonly used.
Then there is an animal-derived thyroid medication, sometimes called desiccated thyroid extract, which is commonly marketed as Armour Thyroid, NP Thyroid, Nature-Thyroid, and several other names.
These medications are produced from dried, ground animal thyroid glands, with pig being the most common type of animal used.
These animal-derived thyroid medications can be prescribed and dispensed, despite lacking FDA approval, because they were already on the market prior to the 1938 Food, Drug, and Cosmetic Act. The act required that any new drugs be proven safe prior to being marketed but included a “grandfather” clause that exempted drugs that were already on the market, including desiccated thyroid extract.
FDA’s statement reflects guidance from national medical societies, like the American Association of Clinical Endocrinology, according to Bridgeman.
Safety concerns
Generally, thyroid hormone replacement medications have a narrow therapeutic index and require thoughtful dosing and monitoring. Because the animal-derived thyroid medications have not been reviewed by FDA for safety, purity, and potency, the statement explains that there may be quality and dosing issues with these products.
Tablets made from the same batches may not have consistent thyroid hormone levels, which could have serious consequences for patients. The medications derived from animal thyroid glands also have an increased risk of certain impurities, potentially leading to infections and other health concerns.
On the front lines
In order to give patients time to transition to an alternative medication, FDA is not taking immediate action against manufacturers who make unapproved animal-derived thyroid medication.
Bridgeman said pharmacists—being on the front lines—can help patients learn about this anticipated change and the potential product discontinuation.
“Providing education to patients and their health care providers is a key strategy for ensuring safe and effective transition to alternative treatments for managing hypothyroidism. Additionally, pharmacists are poised to remind patients of some of the benefits of the synthetic levothyroxine formulations to provide reassurance in the context of product discontinuation. It’s a good opportunity to underscore medication administration strategies to support consistency and adherence with medication use,” she said. ■
Refresh your knowledge on how to treat hypothyroidism
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The thyroid disorders module contains information on guidelines and landmark trials, treatment goals, disease state management, monitoring and follow up, practical clinical management tips, and more. You can also assess your knowledge with case-based learning exercises and self-assessments. To access PharmacotherapyFirst, visit https://pharmacylibrary.com/pharmacotherapyfirst. ■