Response to the FDA's August 2025 statement on Desiccated Thyroid
The FDA posted a statement last week warning about the use of desiccated thyroid (DTE), making unsubstantiated claims about DTE and stating they have “concerns with the safety and effectiveness of the unapproved animal-derived thyroid medications”.
I find the discussion surrounding desiccated thyroid both perpetually fascinating and, at times, profoundly frustrating due to persistent misconceptions. The evidence surrounding the use of desiccated thyroid is quite clear and this recent statement made by the FDA provides very strong evidence, in my opinion at least, that the FDA does not base its guidelines on evidence-based research.
The Importance and Benefits of Desiccated Thyroid
Desiccated thyroid, derived from porcine thyroid glands, is a natural thyroid product that contains a spectrum of thyroid hormones: T1, T2, T3, and T4, in concentrations similar to what is naturally found in humans. This multi-component nature is a key aspect of its importance and perceived benefits.
Its principal benefits, extensively documented in both clinical experience and a growing body of literature, revolve around symptom improvement and overall quality of life, particularly when compared to therapies that rely solely on T4. Patients often report feeling and functioning significantly better on desiccated thyroid.
Beyond subjective well-being, desiccated thyroid has been shown to exert profound metabolic effects:
Reduces visceral fat. This is a critical point, as visceral fat is implicated in numerous chronic diseases, and T3 (a key component of desiccated thyroid) directly influences its reduction.
Improves lipid profiles by lowering cholesterol (including LDL and ApoB) and triglycerides, and raising beneficial HDL cholesterol. Some sources state that these effects are not achievable with statins.
Lowers blood sugar and improves insulin sensitivity, helping to prevent and potentially reverse type 2 diabetes.
Enhances metabolism and can contribute to weight loss.
Improves cognitive function and memory.
Alleviates fatigue and depression, often proving more effective than conventional antidepressants in some cases.
Resolves constipation and other issues related to bowel function.
Why Desiccated Thyroid is More Beneficial than Levothyroxine
The core of desiccated thyroid's perceived superiority lies in the presence of T3 (liothyronine) in addition to T4 (levothyroxine). Levothyroxine (Synthroid, Levoxyl) is a T4 monotherapy. The assumption behind T4 monotherapy is that the body will efficiently convert T4 into the active T3 hormone in the periphery. However, this conversion process is often inefficient, ineffective, or blocked in many individuals due to various factors including certain enzyme polymorphisms or non-thyroidal illnesses.
Here's why desiccated thyroid, or at least the inclusion of T3, is considered more beneficial:
T3 is the Active Hormone: T3 is the biologically active form of thyroid hormone at the cellular level, responsible for regulating gene expression, metabolism, and overall cellular function. T4 is essentially a pro-hormone.
Inadequate T3 Conversion on T4 Monotherapy: Many patients on T4 monotherapy, despite having "normal" TSH and T4 levels, continue to experience hypothyroid symptoms like fatigue, weight gain, and depression because their bodies are not adequately converting T4 to T3. This is referred to as "functional hypothyroidism" or "thyroid deficiency" where TSH is normal but symptoms persist.
Direct T3 Supply: Desiccated thyroid provides a direct supply of T3, ensuring its availability to tissues and cells, which can lead to significant symptomatic improvement even when TSH is suppressed. Some studies indicate that T4 can actually suppress the body's own T3 production by inhibiting the 5'-deiodinase enzyme.
Comprehensive Hormonal Profile: The presence of T1 and T2 in desiccated thyroid, which are absent in synthetic T4/T3 combinations, is posited to contribute to its better symptomatic improvement and a "smoother" thyroid reaction in the body, although the exact mechanisms are not fully understood.
Patient Preference: Numerous studies and clinical observations indicate that patients prefer combination therapy (T4/T3) or desiccated thyroid over T4 monotherapy for improved quality of life, mood, and cognitive function.
What the Research Shows About Desiccated Thyroid
Research on desiccated thyroid, while often challenged by the prevailing T4-centric guidelines, consistently points to several key findings:
Efficacy for Symptoms: Studies, including randomized controlled trials and meta-analyses, show that desiccated thyroid improves symptoms (e.g., fatigue, depression, weight, cholesterol, cold intolerance) often above and beyond T4 alone or even synthetic T4/T3 combinations.
"Super Physiologic" Dosing and Safety: Surprisingly, studies utilizing "super physiologic" doses of T3 (a component of desiccated thyroid) have shown significant therapeutic effects without the typical signs of thyrotoxicosis like palpitations or jitteriness, as long as the dose is carefully monitored and adjusted. This challenges the long-held fear of TSH suppression, as many studies demonstrate no harm in suppressing TSH with exogenous thyroid hormone replacement if T3 and T4 levels are within a reasonable range and clinical symptoms are managed.
Lack of Cardiovascular Risk: Despite concerns often raised by traditional endocrinology, direct research, particularly on high-dose thyroid, indicates a low cardiovascular risk. Equating prescribed high-dose thyroid with endogenous hyperthyroidism (Graves' disease) is considered a myth and an inaccuracy. The latter is an autoimmune disease with different underlying pathophysiology and associated risks not seen with exogenous hormone replacement.
No Increased Osteoporosis Risk: Another pervasive myth is that thyroid treatment, especially at higher doses, causes osteoporosis. Extensive research, including studies on thyroid cancer survivors who often receive TSH-suppressive doses, has refuted this claim, showing no significant increase in osteoporosis or fractures with exogenous thyroid hormone replacement. The primary factor in bone loss is menopausal status and estrogen deprivation, not properly managed thyroid therapy.
Guidelines are Outdated/Biased: Multiple sources highlight that current guidelines from professional societies (e.g., American Thyroid Association, AACE) are outdated, political, and biased against desiccated thyroid and T3-containing regimens, often influenced by pharmaceutical company marketing. These guidelines often rely on flawed studies or misinterpretations of data. Many experts advocate for the elimination of TSH as the sole biomarker for monitoring therapy, favoring T3 and clinical parameters.
Why the FDA Statement is Not Evidence-Based
The FDA's statement, "Due to their complex biological origin, desiccated thyroid contains many compounds that are uncharacterized for safety and effectiveness," directly contradicts a significant body of evidence and historical use:
Long History of Use: Desiccated thyroid has been in clinical use for over 100 years. To suggest its compounds are "uncharacterized" ignores a century of practical application and observation. Its historical use for affective disorders dates back to the 1930s.
Known Components: As a natural product derived from the pig thyroid gland, its primary active components (T1, T2, T3, T4) are well-known thyroid hormones with established physiological roles and metabolic properties in the human body. While T1 and T2 might not be as extensively researched as T3 and T4, their presence contributes to the "whole-gland" effect that many clinicians and patients find beneficial.
Manufacturing Standards: The notion that it contains "uncharacterized" and potentially unsafe compounds due to its "complex biological origin" is contradicted by the fact that desiccated thyroid products (like NP Thyroid or Armour Thyroid) are manufactured and assayed per established FDA manufacturing standards and USP monographs. This ensures that the T3 and T4 content consistently complies within strict parameters, with any deviation leading to batch rejection. Claims of "batch variability" from decades ago have been refuted by modern manufacturing and regulatory oversight. In fact, one source notes that Synthroid, a synthetic T4 product, has had more recall problems than desiccated thyroid products.
Lack of Harmful Studies: Crucially, there are no studies showing harm from desiccated thyroid use, despite the prevailing narrative and warnings. Many studies, as detailed above, demonstrate its safety and efficacy, particularly when contrasted with the known risks of alternative psychiatric medications (in cases of mood disorders where HDT is used).
Political and Economic Agendas: The resistance to desiccated thyroid and the FDA's cautionary stance appear to be strongly influenced by political and economic agendas, particularly from manufacturers of synthetic T4 products. These entities have historically marketed against desiccated thyroid, leveraging influence with insurance companies and guideline-setting bodies to prioritize T4 monotherapy, despite evidence of its suboptimal effectiveness for many patients. This creates a situation where robust positive data for desiccated thyroid is often "ignored" or "suppressed" by official bodies.
In essence, the FDA's statement, while seemingly cautious, does not align with the comprehensive historical experience, the known physiological roles of desiccated thyroid's components, or the substantial body of research demonstrating its safety and efficacy. It reflects a cautious stance rooted in a regulatory framework that sometimes struggles to evaluate complex biological products against chemically isolated pharmaceuticals, often overlooking real-world clinical outcomes and the nuances of individual patient responses.
- Luke Swift, DNP, APN-FPA, PMHNP-BC, ABHRT
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