Thyroid Extract Interactions Overview

Additional Information

Is Thyroid Extract Safe? Are There Any Warnings?

Thyroid extract, derived from animal thyroid gland tissue, can be potentially unsafe when taken as a dietary supplement and not under the supervision of a healthcare provider. Supplements contain triiodothyronine (T3) and thyroxine (T4), but the varying potency of these hormones makes dosing challenging. Using thyroid extract increases the risk of hyperthyroidism and related cardiac and neurological complications.

It is generally recommended to only take thyroid hormones under the supervision of a medical provider so you can have appropriate labs ordered and be monitored.

How Does Thyroid Extract Work? What Is the Mechanism of Action?

Thyroid extract is derived from animal thyroid gland tissue and contains both triiodothyronine (T3) and thyroxine (T4). However, the potency of these hormones may vary among different brands of thyroid extract, and it also contains thyroglobulin, inactive metabolites, and impurities.

The thyroid hormones T3 and T4 found in thyroid extract play a vital role in regulating metabolic functions, controlling growth and development, and influencing various physiological processes. These hormones regulate metabolic rate, fluid and electrolyte balance, nutrient metabolism, and the maturation of bones and the brain.

Pharmacokinetics

Thyroid extracts contain both T4 and T3.

The absorption of T4 (levothyroxine) in the gastrointestinal tract is a complex process, influenced by multiple factors. These factors include the method of administration and the composition of the intestinal environment, which encompasses aspects like the gut microbiome, plasma proteins, and dietary elements.

The absorption rate can vary within a range of 48% to 79% of the administered dose, with fasting (i.e., taking on an empty stomach) generally improving absorption. However, conditions such as malabsorption syndromes and specific dietary factors, like the use of children's soybean formula or anionic exchange resins such as cholestyramine, can lead to excessive excretion of thyroid hormones in the feces.

In contrast, liothyronine (T3) exhibits high absorbability, with roughly 95% being absorbed within four hours. Both natural thyroid hormone preparations and synthetic counterparts are assimilated in similar ways.

More than 99% of these circulating thyroid hormones attach to serum proteins, including thyroid-binding globulin (TBg), thyroid-binding prealbumin (TBPA), and albumin (TBa). These proteins differ in their capacities and affinities for thyroid hormones.

Levothyroxine (T4) has a stronger affinity for both TBg and TBPA compared to liothyronine (T3), contributing to its higher serum levels and longer half-life. The small fraction of free hormones in equilibrium with protein-bound hormones governs metabolic activity.

The deiodination of levothyroxine (T4) occurs in various tissues, including the liver and kidney. Conjugated forms of the hormone, as glucuronide or sulfate, are found in the bile and gut, potentially participating in enterohepatic circulation. Approximately 85% of daily metabolized levothyroxine (T4) undergoes deiodination in this process.

Interaction Overview (See Bottom of Page For Full List)

With Drugs: Thyroid extract may interact with several drugs including other thyroid hormones, insulin, and estrogens.

Common Side Effects To Watch For

When taken orally, thyroid extract may lead to elevated levels of triiodothyronine (T3) and/or thyroxine (T4), which can cause flushing, increased heart rate, weight loss, shivering and sweating. Serious adverse effects are rare but may include thyroid storm or thyrotoxic crisis.

Are Supplements Standardized?

Laboratory analysis shows a wide variation in the amount of thyroid hormones in commercially available thyroid extract products. Some contain measurable amounts of T3 and T4, while others do not. Standardization is limited, making dosing consistency a challenge.

What Is Thyroid Extract Typically Used For?

Hypothyroidism: While there has been interest in using oral thyroid extract for hypothyroidism, there is insufficient reliable information about its clinical effectiveness for this purpose.

Drugs that interact with Thyroid Extract