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April 24, 2023 12 min read

If you're here, chances are you're no stranger to the challenges of navigating through hypothyroidism. And one of the biggest challenges can be understanding all of the medical jargon that comes along with it. From TSH to FT4, FT3 to NDT, it can feel like you need a degree in endocrinology just to keep up. But don't worry - we've got you covered. In this article, we'll break down some of the most common thyroid-related terminologies you'll likely encounter during your journey toward managing hypothyroidism.

Whether you're newly diagnosed, or you've been dealing with hypothyroidism for years, understanding these terms will help you feel more informed and empowered when it comes to your health. So, let's dive in!

The thyroid gland

To grasp the meaning behind "thyro" medical terms, let's start by understanding the star of the show—your thyroid gland! Resembling a butterfly in appearance and strategically positioned at the front of your neck, this vital gland serves a multitude of indispensable functions in maintaining overall health and well-being. Among its numerous responsibilities is the regulation of metabolism, ensuring stable temperature control, managing heart rate, and coordinating diverse physiological processes essential for smooth body function.

The endocrine system

The thyroid is part of the endocrine system, which comprises a complex network of glands and hormones responsible for regulating your body's internal environment and maintaining homeostasis—a delicate balance of conditions vital for cells and organs to function properly. This system oversees various critical functions, including growth, development, metabolism, sexual function, and stress response.

The thyroid hormones

As part of the endocrine system, your thyroid plays is responsible for producing and releasing the following hormones.

Thyroxine (T4)

Thyroxine (T4) is an essential hormone produced and released by your thyroid gland. Your thyroid gland produces around 80% T4. But although the gland mainly produces T4, this hormone doesn't have a significant impact on your metabolism.

T4 exists in two forms within the body: free T4 and bound T4. Free T4 can travel to body tissues that utilize it, while bound T4 sticks to proteins that keep it from entering these tissues. In fact, over 99% of T4 is found in its bound form.

Your body converts T4 into T3 by enzymes called deiodinases in various body parts like the liver, kidneys, and muscles.

Triiodothyronine (T3)

Triiodothyronine (T3) is the active form of thyroid hormone. Your thyroid gland only produces around 20% of T3. While the thyroid produces a smaller amount of T3 compared to T4, it has a more significant impact on boosting metabolism. T3 is vital for many processes like metabolism, heart rate, and overall growth and development.

It's important to note that your body can only use T3. That's why T4 needs to be converted into T3.

T4 and T3 are often collectively called "thyroid hormone."

Reverse triiodothyronine (RT3)

In addition to transforming into T3, a small portion of T4 is also converted to a hormone called reverse triiodothyronine (RT3) by enzymes in your brain and placenta. RT3 is considered the non-active form of T3, meaning it doesn't have a metabolic effect. Although RT3 has the same number of iodine molecules as T3, they are attached to different locations within the hormone.


This hormone helps maintain the perfect balance of calcium in your blood.

Other hormones

In addition to the more prominent T3 and T4 hormones, your thyroid also produces lesser-known hormones called T1 and T2. Although not as extensively researched or understood as their counterparts, these hormones play a role in maintaining overall thyroid function and contribute to the wide-ranging effects of thyroid hormones on your body.

How does your thyroid make its hormones?

To make these hormones, your thyroid needs iodine—an essential element found in food (like iodized table salt) and water. Your thyroid captures iodine and transforms it into those fantastic hormones. Just remember that having too much or too little iodine can affect how well your thyroid works its magic.

The roles of thyroid hormone

Thyroid hormone (T4 and T3) play a crucial role in various body functions such as:

  • Energy usage (metabolism)

  • Heart rate

  • Breathing

  • Digestion

  • Body temperature regulation

  • Brain development

  • Mental activity

  • Skin and bone maintenance

  • Fertility.

Other organs that interact with your thyroid gland

You might hear about so many other organs besides the thyroid gland itself as you learn more about your thyroid health. Well, as part of the endocrine system, your thyroid works together with other glands and hormones to keep you feeling your best. Some hormones depend on others to start working, and sometimes hormones can even suppress each other.

But don't worry. Your body has a pretty cool system for keeping your hormones in check. Your thyroid works together with other endocrine glands, mainly the hypothalamus and the pituitary gland.

The hypothalamus, a part of your brain located on the undersurface, secretes thyroid-releasing hormone (TRH) to get your pituitary gland to release thyroid-stimulating hormone (TSH). TSH then tells your thyroid follicular cells to release thyroxine (T4) and triiodothyronine (T3) as long as there are adequate levels of iodine in your body.

Now, let's talk about all the organs and systems in your body that are affected by your thyroid hormones. Almost all of your organ is affected by the thyroid and its hormones. These include:

  • Your nervous system is impacted by the thyroid. If your thyroid isn't working properly, you might experience symptoms like numbness, tingling, pain, or a burning sensation in affected parts of your body. And don't forget that hypothyroidism can lead to depression, while hyperthyroidism can cause anxiety.

  • Your heart is one of the big ones affected by the thyroid. Your thyroid helps regulate your heart's cardiac output, heart rate, and even the strength and vigor of your heart's contractions.

  • The thyroid is involved in how food moves through your digestive system, too. It helps regulate gastrointestinal motility, which can cause digestion problems if your thyroid isn't functioning properly.

  • Last but not least, let's talk about the reproductive system. If your thyroid isn't working properly, it can cause irregular menstrual periods and issues with fertility.

The most common thyroid diseases

A woman consulting about thyroid health and hypothyroidism in an endocrinologist office.

Thyroid disorders and diseases Are very common, especially in women. The most common issues that can affect the thyroid are as follows:


Hypothyroidism, also known as underactive thyroid, occurs when your thyroid gland doesn't produce enough thyroid hormone to meet your body's needs adequately. Low thyroid hormone levels lead to symptoms like fatigue, sensitivity to colds, constipation, dry skin, memory problems, and weight gain. If left untreated, hypothyroidism can lead to more severe health issues such as heart problems, nerve damage, or even infertility.

Hypothyroidism frequently results from Hashimoto's thyroiditis, a thyroid surgery to remove part or the entire thyroid gland, or harm sustained during radiation therapy. Additional causes include:

  • Inflammation of the thyroid (thyroiditis)

  • Congenital hypothyroidism, which implies the condition is present at birth

  • Insufficient iodine intake

  • Disorders of the pituitary gland or hypothalamus

  • Certain medications, such as those for heart conditions, cancer treatments, and drugs for bipolar disorder.

Moreover, your likelihood of developing hypothyroidism may increase if you are living with other health issues like celiac disease, type 1 or 2 diabetes, rheumatoid arthritis, or lupus.

You've likely heard that there are different types of hypothyroidism, and it can be rather confusing, but let us break down the most common ones for you in simple sentences:

  • Subclinical hypothyroidism refers to mild thyroid failure with slightly elevated TSH levels but normal levels of T3 and T4. Patients may experience mild symptoms or none at all. It's essential to monitor subclinical hypothyroidism since it can progress to full-blown hypothyroidism if left unaddressed.

  • Overt hypothyroidism is a more severe form of the condition characterized by high TSH levels along with low free T3 and free T4 levels leading to noticeable symptoms.

  • Central (or secondary) hypothyroidism occurs when the pituitary gland doesn't send adequate signals (TSH), leading to insufficient hormone production.


Hyperthyroidism, also known as overactive thyroid, occurs when your thyroid gland is too active and produces too much thyroid hormone. Symptoms of hyperthyroidism include increased heart rate, weight loss, heat sensitivity, muscle weakness, and irritability. Understanding the differences between these conditions can help you navigate conversations with healthcare providers.

Hashimoto's disease

Hashimoto's thyroiditis, also known as chronic lymphocytic thyroiditis, is the leading cause of hypothyroidism in the United States. It occurs when your immune system mistakenly attacks your thyroid gland, gradually diminishing its ability to produce hormones.

In some cases, people with mild Hashimoto's may not experience any noticeable symptoms, and the condition could remain stable for years. Its symptoms can be subtle and unspecific, which means they can mimic those of other conditions.

Symptoms of Hashimoto's thyroiditis can include fatigue, depression, constipation, mild weight gain, dry skin, pale face, cold intolerance, and enlarged thyroid (goiter).

Having other autoimmune diseases, such as celiac disease or inflammatory bowel disease, can increase your risk of Hashimoto's disease.

Grave's Disease

Graves' disease, named after the doctor who first identified it over 150 years ago, is a prevalent cause of hyperthyroidism in the United States, affecting approximately 1 in 200 individuals.

This autoimmune disorder occurs when your body's immune system erroneously targets your entire thyroid gland. As a result, the gland overproduces hormones essential for metabolism regulation. Graves' disease has significant effects on the normal functioning of your thyroid and overall health.


Goiter refers to a noncancerous swelling of the thyroid gland. The most prevalent cause of goiter globally is a lack of iodine in one's diet. About 15.8% of the world's population experiences goiter, with the percentage varying and being more common in regions where iodine deficiency is widespread. In the United States, around 4.7% of people are affected by goiter.

Goiter can impact anyone at any age, particularly in areas where iodine-rich foods are scarce.

Though iodine deficiency is a major cause, it's not responsible for all cases of goiter. Other factors contributing to goiters include Graves' disease, congenital hypothyroidism, thyroiditis, and pituitary gland tumors.

Thyroid nodules

Thyroid nodules are growths that emerge on or within your thyroid gland. While the specific causes often remain unknown, they can include factors such as iodine deficiency and Hashimoto's thyroiditis. These nodules can be either solid or fluid-filled.

Though most nodules are benign, a small percentage may be cancerous.

In most cases, thyroid nodules don't exhibit any symptoms. However, if they grow significantly in size, they can cause neck swelling, leading to issues like breathing and swallowing difficulties, pain, and goiter.

Thyroid cancer

This is a type of cancer that affects the cells on your thyroid. Many cases of this thyroid disorder are asymptomatic. People usually find out they have it during a regular check-up or testing for something else. As thyroid cancer grows, you might notice the following:

  • A bump you can feel through your neck's skin

  • Feeling like shirt collars are becoming too snug

  • Your voice getting more hoarse over time

  • Trouble when swallowing

  • Swollen lumps in your neck area (lymph nodes)

  • Pain in your neck and throat

So, why does this happen? Cancer cells pop up when some changes occur in the normal cells of the thyroid. These changes, called mutations, make the cells grow super fast and stay alive way longer than healthy ones. Over time, these "bad" cells pile up and form a mass called a tumor.

This tumor can then spread to nearby tissues or lymph nodes in the neck. Sometimes, cancer cells might even go beyond the neck to other body parts like bones or lungs. Figuring out what causes these cell changes remains unclear for most thyroid cancers.

There are different types of thyroid cancer, including Papillary thyroid cancer, Follicular thyroid cancer, Medullary thyroid cancer, and Anaplastic thyroid cancer.

What are the tests to diagnose thyroid disorders?

Other things you'll come across when it comes to managing thyroid health are the different tests. Here's what some of them mean.

TSH test

The TSH (thyroid-stimulating hormone) test is a blood test that checks the amount of TSH in your body. As we've mentioned earlier, TSH is responsible for controlling your thyroid, and it's made by the pituitary gland. When there's too much thyroid hormone, the pituitary gland takes a break and makes very little TSH or stops completely. But if there isn't enough thyroid hormone, the pituitary gland kicks into action and makes more TSH to get your thyroid working harder.

So, the results of a TSH test can reveal if you have hypothyroidism or hyperthyroidism. High TSH levels typically point to hypothyroidism, while low levels suggest hyperthyroidism.

Free T4 test

This test checks the amount of free T4 (FT4), or free thyroxine, in your blood. So, what's free T4? Well, some T4 in your blood sticks to proteins, while other T4 floats around freely without being attached to proteins. That floating T4 is what we call free T4.

Testing for this unbound T4 is more accurate than checking for the protein-bound version. In most cases, this test is done to confirm TSH test results. Low levels of FT4 may indicate hypothyroidism, while high levels may mean that you have hyperthyroidism.

Free T3 test

Similar to the free T4 test, the free T3 test measures the amount of T3 that doesn't attach to anything. It's often ordered together with T4 and TSH tests.

TPO Antibody Test

A TPO antibody test is a blood test that checks for thyroid peroxidase (TPO) antibodies, which are proteins made by your immune system that mistakenly attack the enzyme crucial for producing thyroid hormones. This test helps diagnose autoimmune thyroid disorders like Hashimoto's thyroiditis or Graves' disease, monitor treatment effectiveness, and identify potential risks during pregnancy. Although it's not as common as the other tests, it also plays a key role in understanding your thyroid health and guiding healthcare providers toward appropriate treatments or interventions.


A biopsy is usually only performed if your doctor or endocrinologist suspects thyroid cancer. During a thyroid biopsy, a small tissue sample is taken from the thyroid gland and analyzed in the lab. This procedure is usually done when a nodule or mass has been found in the thyroid to help determine if it's cancerous or benign.

What are the treatments for thyroid problems?

Hypothyroidism: Thyroid hormone replacement therapy

Thyroid hormone replacement therapy is a treatment used to compensate for inadequate thyroid hormone production in individuals with an underactive thyroid. This therapy involves administering synthetic or animal-derived thyroid hormone to substitute for the hormones that the body fails to produce sufficiently.

Thyroid hormone replacement therapy serves to alleviate symptoms of hypothyroidism, such as fatigue, weight gain, depression, and sensitivity to cold temperatures. By providing the body with the required thyroid hormones, this therapy helps normalize metabolic functions, making it an essential treatment for individuals with an underactive thyroid gland.

1. Levothyroxine (Synthetic T4)

Levothyroxine is the most common form of thyroid hormone replacement therapy that involves using a synthetic version of the thyroid hormone thyroxine (T4). The body then converts this T4 hormone into triiodothyronine (T3), the active thyroid hormone. Some of the most popular brand names of levothyroxine are Synthroid, Levoxyl, and Tirosint.

2. Liothyronine (Synthetic T3)

Sometimes, a synthetic form of the T3 hormone (Liothyronine) is added to T4 therapy to provide a more balanced thyroid hormone replacement. Examples of liothyronine are Cytomel and compounded T3.

Liothyronine is generally prescribed to people who cannot tolerate levothyroxine or whose bodies do not convert T4 to T3 effectively. It may be used alone or in combination with levothyroxine. However, liothyronine is generally not the first-line treatment for hypothyroidism.

3. Natural desiccated thyroid (NDT)

Natural desiccated thyroid (NDT) was the first available medication for hypothyroidism. The use of levothyroxine has reduced its utilization, but in recent years, it has been experiencing a resurgence in popularity.

Also known as desiccated thyroid extract (DTE), NDT is a thyroid hormone replacement therapy that is derived from the desiccated (dried) thyroid glands of pigs. It contains both T4 and T3 hormones instead of just one, like levothyroxine and liothyronine.

NDT works similarly to synthetic thyroid hormone replacement therapies by providing the body with the T4 and T3 hormones it requires. However, the unique aspect of NDT is that it comes from animal sources, which means it's a more "natural" and biologically compatible source of thyroid hormones. The body efficiently absorbs NDT, using the T4 and T3 hormones to regulate metabolism, energy levels, growth, and development. That's why many people see NDT as the more effective treatment. One research also found that most people prefer NDT compared to levothyroxine.

Some of the most popular NDT brands in the US are Armour Thyroid, NP Thyroid, Nature-Throid, and WP Thyroid. Unfortunately, some of these brands are no longer in production.

You can also buy desiccated thyroid online, without a prescription, such as VitaliThy. Despite being categorized as a supplement, it provides the same benefits as NDT medications. The reason for this classification difference is due to the contrasting laws between the US and Vietnam. VitaliThy, a natural desiccated thyroid you can buy online, is also free of lactose, gluten, artificial coloring, artificial flavoring, eggs, fish, and shellfish.

Treatments for Hyperthyroidism

  1. Anti-thyroid medications: These drugs work by impeding the production of thyroid hormones, effectively controlling hyperthyroidism.

  2. Radioactive iodine: A popular treatment that involves using a radioactive form of iodine to damage the thyroid gland, thereby reducing its hormone production.

  3. Surgery: Surgical removal of part or all of the thyroid gland, known as thyroidectomy, is another option to treat hyperthyroidism.

Treatments for Thyroiditis

  1. Pain relievers: Nonsteroidal anti-inflammatory drugs (NSAIDs) might be prescribed to alleviate pain and inflammation in the thyroid gland.

  2. Hormone replacement: Depending on the type of thyroiditis, hormone replacement therapy may be required if hypothyroidism develops.

Treatments for Goiter

  1. Watchful waiting: If the goiter is small and not causing any symptoms, the healthcare provider may simply monitor it regularly.

  2. Medications: In some cases, hormone replacement therapy may help shrink the goiter.

  3. Surgery: Removal of all or part of the thyroid gland is an option for large goiters that cause breathing or swallowing difficulties.

Treatments for Thyroid Cancer

  1. Surgery: The primary treatment for thyroid cancer is the surgical removal of the tumor and possibly surrounding tissue or the entire thyroid gland.

  2. Radioactive iodine therapy: This treatment is often used after surgery to destroy any remaining cancer cells.

  3. Hormone therapy: In this case, thyroid hormone replacement is used to prevent the TSH from stimulating further cancer growth.

  4. External radiation therapy: Radiation therapy can be employed if cancer has spread to other areas.

  5. Chemotherapy: In more aggressive cases, chemotherapy may be necessary to treat thyroid cancer.

Conclusion: Advocate for your thyroid health

Now that you've been introduced to some thyroid-related medical terms, you're better equipped to advocate for your health and converse with healthcare professionals more confidently regarding thyroid diseases. Continue nourishing your knowledge about thyroid function, and consider sharing what you learned today with someone who may benefit from this information too!

Wojciech Majda
Wojciech Majda

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