How Thyroid Hormone Replacement Evolved: From DTE to T4 and T3

Did you know the history of thyroid hormone replacement stretches back more than 130 years, to a time before physicians could measure TSH or distinguish T4 from T3?

It began with animal-derived preparations. Levothyroxine later became the standard medication for most adults with primary hypothyroidism, yet desiccated thyroid extract remains part of provider and patient conversations.

How did thyroid care reach this point, and what led levothyroxine to become the predominant approach?

Why Thyroid Medication History Is Important in 2026

This history is newly relevant as the FDA addresses the regulatory status of animal-derived thyroid products. The FDA currently considers marketed desiccated thyroid products to be unapproved biological products that are not eligible for compounding and has outlined a risk-based enforcement approach while additional guidance is developed.

How DTE, T4, and T3 Changed Thyroid Hormone Replacement

To understand how today's thyroid medication practice developed, this Strive Sessions webinar explores questions such as:

• Why did thyroid replacement begin with animal-derived preparations?
• Which developments shifted the prevailing model toward synthetic T4?
• How did laboratory testing change the evaluation of thyroid replacement?
• Why does desiccated thyroid extract (DTE) remain part of the conversation?
• What does this history reveal about standardization and individualized care?

The full session covers the discoveries and clinical shifts that moved thyroid replacement from whole-gland preparations toward modern hormone-specific medications and testing.

Watch How DTE, T4, and T3 Shaped Modern Thyroid Medication

Recording note: This session reflects the regulatory information available at the time of recording. Refer to the FDA’s current animal-derived thyroid communications for the latest agency information.

Take a Deeper Dive Into Thyroid Hormone Replacement

After watching, read Andrea Daniels’ provider guide for more detailed information about current thyroid medications, DTE transitions, monitoring, and regulatory considerations.

Read Andrea Daniels' guide: Thyroid Hormone Replacement: DTE, T4/T3 Options, and Transition Considerations for Providers

Thyroid Hormone Replacement Began With Animal-Derived Preparations

In 1891, British physician George Murray reported using sheep thyroid extract for a patient with myxedema, a severe manifestation of hypothyroidism. The experiment occurred before the hormones within the thyroid gland had been isolated and before modern laboratory testing could show providers what was changing physiologically.

Without hormone assays or other modern laboratory testing, early clinicians faced fundamental questions that modern providers rarely encounter. How were early thyroid preparations evaluated? What did clinicians think they were replacing? And what changed once researchers could study the thyroid as a system of distinct hormones rather than as a single glandular substance?

What followed was not one decisive discovery. Advances in hormone isolation, manufacturing, and laboratory testing gradually changed how clinicians understood and evaluated thyroid replacement.

How T4, T3, and Laboratory Testing Changed the Conversation

The isolation of T4 and later identification of T3 gave clinicians a different vocabulary for thyroid replacement. Improved laboratory testing added another dimension: providers could increasingly evaluate specific hormones and regulatory signals rather than relying primarily on symptoms, physical findings, or indirect measurements.

But which development most influenced the rise of levothyroxine? Did it rise because of hormone isolation, improved manufacturing, TSH testing, or a better understanding of T4-to-T3 conversion? The answer cannot be reduced to one development.

A review of the changing approaches to hypothyroidism management examines how new testing methods and changing knowledge of thyroid physiology influenced clinical practice.

How “Natural” and “Synthetic” Became Thyroid Medication Categories

Modern discussions often divide thyroid medications into “natural-derived” and “synthetic” categories. Historically, the distinction emerged from the order in which these medications developed.

Animal-derived preparations came first because isolated thyroid hormones weren’t yet available. Synthetic T4 and T3 became possible only after researchers identified and learned to produce the individual hormones.

The labels describe how these medications originated, not how they perform clinically. DTE and synthetic thyroid hormones emerged under very different scientific and manufacturing conditions. They do not determine which medication is appropriate for an individual patient.

Three Questions Behind the Evolution of Thyroid Hormone Replacement

1. What causes a prevailing clinical model to change?

No single discovery moved thyroid care from gland-derived preparations toward synthetic hormones. The session examines how research, manufacturing, laboratory testing, and clinical practice contributed to that shift.

2. What does improved measurement clarify and what can it leave unresolved?

Measuring T4, T3, and TSH gave clinicians information that earlier generations did not have. It also changed how thyroid replacement was evaluated and adjusted.

3. How should standardization and individualized care coexist?

DTE predates synthetic thyroid hormones but has not disappeared from provider and patient discussions. Its continued presence raises questions about standardization, patient experience, and individualized care that cannot be resolved by the terms “natural-derived” and “synthetic” alone.

These questions are more useful than a simplified contest between old and new. They reveal why the evolution of thyroid hormone replacement still deserves provider attention and why the complete historical discussion is difficult to capture in a short article.

“No two patients are the same, and no two patients’ thyroid stories are the same.” - Andrea Daniels, PharmD

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Disclaimer:

This information is intended for educational purposes only and does not constitute medical advice. The information in this blog article is not intended as a substitute for professional medical advice, diagnosis, or treatment. Never disregard professional medical advice or delay seeking medical attention because of something you have read in this blog article. The creators of this content disclaim any liability for decisions made based on the information presented.

Consult your healthcare provider before starting any prescription medications, dietary supplements, or skincare products. Always seek the advice of your healthcare provider for any questions you may have regarding a medical condition. Certain medications may interact with your current prescription medications, medical conditions, or other supplements. Your healthcare provider can provide guidance tailored to your specific health needs.

Compounded medications are specially prepared for identified individual patient needs based on a valid prescription from a prescribing healthcare practitioner and, as such, have not been reviewed or approved by the U.S. Food and Drug Administration (FDA) for safety or efficacy.. The statements in this article have not been evaluated by the FDA.