You may have already tried everything—changing your diet, taking medication, endless doctor visits—and yet you still feel tired, drained, frustrated, and simply misunderstood. If this sounds familiar, you’re not alone.

For many people with thyroid issues, it feels as if their body is working against them. Lab results may seem “normal,” but you can sense something isn’t right. One often overlooked cause behind these symptoms could be a so-called conversion disorder, sometimes referred to as a thyroid hormone conversion issue.

But what exactly does that mean? And more importantly, what can you do to bring your body back into balance?

In this article, you’ll find answers to the most important questions about conversion disorders:

• What is a conversion disorder?
• How can I recognize a conversion disorder?
• What are the causes of a conversion disorder?
• And most importantly: What can you actually do to finally regain more energy and quality of life?

Whether you’ve been struggling with these problems for years or are just beginning to explore the topic—we’ll get to know the thyroid better together and show you how to find your path to greater well-being.

The thyroid produces three important hormones that influence numerous body functions. What’s less well-known is that these hormones exist in different forms, and their conversion plays a crucial role in metabolism and overall well-being.

A disruption in this conversion process (conversion disorder) can significantly affect hormonal balance and, despite sufficient hormone production, lead to hypothyroidism.

Below, we’ll take a closer look at the thyroid’s hormones as well as the 3-step thyroid activation system:

The thyroid produces three hormones, including free thyroxine (fT4), free triiodothyronine (fT3), and the hormone calcitonin.

During breakdown and conversion processes, the hormones diiodothyronine (T2) and monoiodothyronine (T1) are also formed, although these are not produced directly by the thyroid itself.

The following steps illustrate how these different hormones work together.

Let’s take a closer look at the thyroid hormones and the 3-step thyroid activation system.

The thyroid mainly produces fT4, an inactive precursor, and only a small amount of fT3, the biologically active hormone that drives metabolism.

fT4 can be converted into fT3, and only then can it activate and regulate metabolic processes.

Most doctors focus their treatment on step 1 by prescribing standard thyroid meds that contain pure T4. However, this is often not enough, and symptoms can persist.

After the thyroid produces fT4, this inactive fT4 must be converted into the active form fT3.

The conversion of fT4 to fT3 takes place mainly in the liver and requires an enzyme called deiodinase, which contains selenium, among other components.

In a conversion disorder, too little fT4 is converted into fT3, which can lead to symptoms of hypothyroidism—even if the thyroid produces enough fT4 or it is taken synthetically in the form of medication.

Active fT3 is carried through the blood to the body’s cells with the help of special transport proteins.

Once there, it can act in different ways. On one hand, fT3 can activate certain genes inside the cells that control important processes in the body. On the other, it can trigger metabolic reactions that affect energy production, fat burning, and the regulation of body temperature.

Only fT3 can bind directly to the cell receptors of target cells (e.g., in the heart muscle, liver, or gut) and regulate metabolism. We’ll take a closer look at this later on.

In a conversion disorder, there isn’t enough fT3 available, which reduces the metabolic processes in the body’s cells. (1)

Conversion disorder is a common but often overlooked cause of thyroid problems. It occurs when the body cannot effectively convert the inactive hormone fT4 into its active form, triiodothyronine (fT3).

T4 is made from the amino acid tyrosine, which is bound to four iodine atoms (hence the name T4), while T3 contains only three iodine atoms. During the conversion process, T4 is transformed into T3.

A key part of this process is the deiodinases—special enzymes responsible for removing one iodine atom from fT4, creating active fT3.

This process is crucial because fT3 is four times more active than fT4 and can bind to the cell receptors of target cells (such as those in the heart muscle, liver, and intestines) to activate and regulate metabolic reactions inside the cells.

fT3 works like a key that fits perfectly into the lock of target cell receptors, triggering a variety of reactions in the cells.

fT4, on the other hand, is like a prepared key that doesn’t yet fit into the lock (receptor) of target cells. It must first be converted into the fitting key, fT3.

This conversion is therefore a critically important step for the entire body. (2)

A lack of fT3 affects the entire body because fT3 is essential for numerous physiological processes.

For example, fT3 promotes the activity and regeneration of mitochondria—the “powerhouses of the cells”—thereby supporting the cells’ energy supply. Along with this comes an influence on body temperature, where fT3 plays a central role in regulation. By activating the mitochondria, fT3 increases not only energy production but also heat generation in these “powerhouses.”

A shortage of fT3 can lead to reduced heat production, which in turn can cause sensitivity to cold. (3)

In addition, fT3 regulates motility—the movement within the intestines. It stimulates the contractions of the smooth intestinal muscles, which are responsible for bowel movements (peristalsis). (4)

These movements ensure that food is transported through the digestive tract. A lack of fT3 can therefore lead to constipation or slowed digestion because the intestines are less active.

To fully understand conversion disorder, we need to look at an important alternative process that’s often overlooked.

In certain situations—such as during high stress or when key nutrients are lacking—the body can produce inactive reverse T3 (rT3) instead of active fT3.

But why is this so significant?

While fT3 is considered the “right key” that easily fits into cell receptors and activates metabolic reactions, rT3 behaves very differently.

rT3 can also fit into the “lock” of the receptors, but this key “won’t turn,” effectively blocking the cell receptors from receiving the important fT3 hormone.

This means that rT3 occupies the receptor meant for active fT3, preventing fT3 from binding and, as a result, stopping metabolic reactions from being activated and regulated.

To identify a conversion disorder, we need to closely analyze both the symptoms and the lab results.

Patients with a conversion disorder often experience classic symptoms of hypothyroidism, even though their lab results may initially appear normal.

Typical symptoms include:

• Fatigue and exhaustion, often regardless of sleep duration or quality
• Weight gain despite consistent diet and activity
• Difficulty concentrating and memory loss
• Hair loss or dry skin
• Sensitivity to cold
• Digestive issues
• Sleep disturbances
• Susceptibility to infections
• Depression
• Infertility
• Menstrual cycle irregularities

These symptoms occur because there isn’t enough active fT3 in the body to adequately stimulate metabolic processes. Since fT3 is the hormone that actually binds to cell receptors and regulates metabolism, the body enters a state of “hypothyroidism” even if fT4 levels are within the normal range. (5)

It’s particularly telling when symptoms such as persistent fatigue, weight gain, or sensitivity to cold continue despite taking thyroid meds. This suggests the body isn’t converting enough fT4 into active fT3, indicating a conversion disorder.

In such cases, it’s advisable not only to look at standard thyroid values but also to specifically analyze fT3 and fT4 to get a more complete picture of thyroid function

A key factor in diagnosing a conversion disorder is taking a closer look at the thyroid hormones in the blood:

• fT4 levels: In a conversion disorder, fT4 levels are often normal because the thyroid produces enough of the hormone—or it’s already being taken in the form of medication.
• fT3 levels: The main indicator of a conversion disorder is a low fT3 level. Since fT3 is the active hormone, a low value shows that the conversion from fT4 to fT3 is impaired.
• rT3 levels: An elevated rT3 level can also be an important sign. As mentioned earlier, rT3 competes with fT3 for binding to cell receptors and blocks fT3’s access. If there’s a high amount of rT3, metabolism is further slowed down.

People often feel uncertain when interpreting their own results. That’s exactly why we developed a value calculator where you can enter your lab results.

It’s important to note that thyroid levels falling merely within the normal reference range are not always enough to relieve symptoms like fatigue or weight gain.

Experience shows that both fT4 and fT3 levels should ideally be in the upper third of the reference range—preferably above 60%. Even if your values are officially “normal,” a subclinical deficiency may be present if they remain at the lower end of the range.

To effectively manage symptoms, a higher value should be the goal.

For example, let’s look at these (fictional) blood values from the miavola Thyroid Masterclass:

These blood values may indicate a conversion disorder because:

• fT3 is only at 22% of the reference range
• fT4 is at 57%
• rT3 is elevated

In many cases, patients with symptoms of hypothyroidism are first prescribed thyroxine (synthetic fT4).

The problem is that in a conversion disorder, the body can’t effectively convert the extra fT4 into fT3. As a result, fT4 levels often continue to rise while fT3 remains low.

This means symptoms often persist, leading to an increase in dosage.

However, overdosing on standard thyroid medication can strain the liver—the organ where much of the thyroid hormone conversion takes place—and lead to increased production of rT3, which can actually make symptoms worse.

Another important point is that consistently elevated fT4 levels over time can damage the heart, as too much fT4 can overstimulate the heart muscle and increase the risk of arrhythmias. (6)

For this reason, when dealing with a conversion disorder, it’s often wise not only to address fT4 but also to consider a targeted fT3 therapy to effectively relieve symptoms and restore balance to the body.

The causes of a conversion disorder are varied, ranging from nutrient deficiencies to autoimmune diseases.

Let’s take a look at some of the key factors that can interfere with the conversion process from fT4 to fT3:

Hashimoto’s thyroiditis is the most common cause of hypothyroidism and can also disrupt the conversion process.

In this autoimmune disease, the immune system attacks the thyroid cells, leading to chronic inflammation and reduced production of thyroid hormones.

This chronic inflammation also affects hormone metabolism, which can impair the conversion of fT4 to fT3.

Patients with Hashimoto’s often have a reduced ability to convert fT4 into fT3, making treatment more complex.

A deficiency in certain nutrients—especially selenium—can severely impair the function of deiodinases, the enzymes responsible for converting fT4 into fT3.

Selenium is an essential trace element that is built directly into the structure of these enzymes. Without enough selenium, the conversion process cannot work efficiently because there aren’t enough functional enzymes, leading to a shortage of active fT3.

A lack of zinc and iron can also affect metabolism and thyroid function.

Glutathione deficiency likewise plays a role in conversion disorders. Our bodies constantly generate oxidative stress as a byproduct of metabolic reactions, producing what are called reactive oxygen species (ROS). ROS are highly reactive molecules that can damage DNA, proteins, and enzymes.

Glutathione—one of the body’s most important antioxidants—plays a key role in protecting against oxidative stress. It’s made from the amino acids glutamic acid, cysteine, and glycine. Glutathione directly neutralizes reactive oxygen species and helps shield cells from the harmful effects of these molecules.

Because of this, glutathione also plays a role in the conversion of fT4 into fT3 by protecting the enzyme 5’-deiodinase, which is particularly sensitive to oxidative stress. As we know, deiodinases are responsible for converting fT4 into fT3.

When glutathione is deficient, 5’-deiodinase cannot work effectively, leading to reduced conversion of fT4 to fT3. To optimally support thyroid function, it’s important to ensure adequate glutathione levels—either through diet or targeted supplementation. (7)

The liver plays a crucial role in the conversion of fT4 to fT3, as most deiodinases are produced there.

Impaired liver function—caused by toxins such as alcohol, medications, environmental pollutants, or fatty liver disease—can disrupt this process.

When the liver is overloaded or damaged, the conversion becomes less efficient, leading to low fT3 levels and the associated symptoms.

Stress has a direct impact on thyroid function and the conversion process.

Under chronic stress, the body produces increased amounts of the hormone cortisol, which can inhibit the conversion of fT4 to fT3 and instead promote the production of reverse T3 (rT3). As a result, less active fT3 is formed, which can worsen the symptoms of hypothyroidism.

Cortisol is produced by the adrenal glands, which are closely connected to the thyroid. (8) (9)

Chronic inflammation and infections in the body can also interfere with the conversion of thyroid hormones.

Inflammatory markers such as cytokines inhibit deiodinases and disrupt the normal metabolism of thyroid hormones.

Gastrointestinal disorders that lead to poor nutrient absorption can also indirectly affect thyroid function. (10)

Hormonal changes, such as an excess of estrogen (for example, in women during pregnancy or from taking the pill), can affect the binding of thyroid hormones to transport proteins.

This reduces the amount of free fT4 available for conversion into fT3, further impairing the conversion process. (11)

The liver plays a central role in the conversion of thyroid hormones, and its health is essential for maintaining hormonal balance in the body.

The majority of inactive thyroid hormone fT4 is converted in the liver into its active form, fT3—about 60% of all fT4 undergoes this process in the liver. This step is crucial for activating metabolism.

A key factor in this conversion is the deiodinases, which remove iodine atoms from fT4 to form fT3. For these enzymes to work efficiently, the body needs selenium, an essential trace element. Selenium is therefore not only important for overall thyroid function but especially for the conversion process in the liver

The liver is not only responsible for converting fT4 to fT3, but also for detoxifying the body and producing bile acids, which are essential for fat digestion.

An overload of the liver from toxins such as environmental pollutants, medications, or alcohol can disrupt this delicate conversion process and lead to an imbalance of thyroid hormones.

This means that even with sufficient fT4 production, the amount of active fT3 available to act on receptors is reduced—resulting in symptoms of hypothyroidism.

It’s clear that thyroid health and liver function are closely interconnected. An imbalance in one of these systems can negatively affect the other. That’s why it’s important to approach thyroid issues systematically rather than just treating the symptoms.

In cases of hypothyroidism, the first step is often prescribing synthetic thyroid meds (fT4). But if a conversion disorder is present, this does little good because the liver cannot effectively convert the additional fT4 into fT3.

Worse still, overloading the liver with synthetic fT4 can strain the heart and cause additional health problems.

If a conversion disorder is present, there are several approaches to help restore thyroid function to balance.

It’s important to take a holistic approach, since multiple factors can contribute to this condition.

The following steps can help support the conversion process from fT4 to fT3:

Since the liver is the primary site for converting fT4 to fT3, it needs to function optimally.

Milk thistle and glutathione can help promote the regeneration of liver cells and protect them from damage caused by reactive oxygen species.

In addition, reducing toxins in the body is essential for optimal liver function. Following a healthy, balanced diet and avoiding environmental toxins and alcohol can help ease the liver’s workload.

Bitter compounds—such as those found in artichoke and dandelion—can also support liver function by aiding detoxification processes and stimulating bile secretion. (12)

Glutathione is an important antioxidant in the body that protects molecules from oxidative stress.

Supplementing with glutathione can help reduce oxidative stress, which in turn may improve the function of deiodinases.

This promotes the conversion of T4 to T3, supporting better thyroid function.

Since selenium plays a crucial role in deiodinase activity, testing blood levels of this trace element is especially important in cases of conversion disorder. (13)

A selenium deficiency can impair deiodinase activity and therefore disrupt the conversion of fT4 to fT3. (14)

Stress increases the production of inactive rT3, which limits the availability of active fT3.

Practices such as yoga, meditation, and breathing techniques can help reduce stress and improve hormone conversion. (15)

In addition to improving the conversion process, synthetic T3 can also be taken directly.

However, it’s important to note that T3 supplements such as Thybon or bioidentical thyroid hormones (natural thyroid extracts from bovine or porcine sources) should always be taken under the guidance of a doctor or in collaboration with a qualified healthcare provider.

In autoimmune diseases such as Hashimoto’s thyroiditis, conversion disorders are common.

A comprehensive treatment approach—one that supports the thyroid while also reducing inflammation—is essential.

This article is based on the latest scientific findings (as of the time of publication, as referenced in the footnotes) and has been reviewed by medical experts. However, it is not intended for self-diagnosis or self-treatment and should not replace a visit to your doctor. Before implementing any measures from this or any other article, please be sure to discuss them with your healthcare provider.