What Is Hypothyroidism?

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Hypothyroidism is a condition in which your thyroid gland—a small, butterfly-shaped gland in your neck—does not produce enough thyroid hormone. It is sometimes referred to as an "underactive" thyroid. Hypothyroidism slows down a person's metabolism, leading to symptoms like weight gain, sluggishness, feeling cold, and more. A simple blood test called thyroid-stimulating hormone (TSH) can diagnose hypothyroidism, and thyroid hormone replacement medication can treat it.

By gaining knowledge about hypothyroidism, including what it feels like to have this thyroid problem, and how it's diagnosed and managed, you will be more prepared and self-assured as you embark on your thyroid journey.

What Is Hypothyroidism?
Verywell / Emily Roberts

Hypthyroidism Symptoms

Your thyroid gland uses dietary iodine to make thyroid hormone. When there is a deficiency in thyroid hormone, your body has trouble using energy and staying warm. Your muscles, brain, and other organs may also have trouble functioning.

The signs and symptoms of hypothyroidism are variable and often subtle. They may be initially misdiagnosed as another condition or even attributed to stress.

Here is a closer look at some of the symptoms a person with an underactive thyroid may experience:

  • Feeling fatigued and exhausted, even after a long sleep
  • Feeling depressed or blue
  • Gaining weight, despite no change in exercise and a healthy diet
  • Experiencing “brain fog” and difficulty concentrating
  • Feeling cold when others feel hot
  • Noticing hair that is coarse and dry, breaking, brittle, or falling out
  • Noticing skin that is coarse, dry, scaly, and thick, especially the soles of your feet
  • An unusually low pulse or blood pressure
  • Slow or sluggish reflexes
  • Puffiness in the face, especially around the eyes
  • High cholesterol levels that are unresponsive to cholesterol-lowering medication
  • Irregular menstrual cycles
  • Experiencing muscle cramps


There are a number of health issues and conditions that cause hypothyroidism.

In the U.S., an autoimmune disease called Hashimoto’s thyroiditis ​is the most common cause of hypothyroidism.

In a person with Hashimoto's, antibodies attack cells in the thyroid gland, making it incapable of functioning properly. Sometimes, this attack causes the thyroid gland to become enlarged.

Antibodies attack thyroid gland cells, affecting function and size.

Post-surgical hypothyroidism refers to insufficient thyroid hormone due to surgical removal of all or part of the thyroid gland. Surgery on the thyroid is known as a thyroidectomy.

Radiation-induced hypothyroidism may occur from radioactive iodine (RAI) therapy, which is used to treat hyperthyroidism and thyroid cancer. Exposure to radiation treatments to the head and neck, or radioactive fallout from nuclear accidents like Chernobyl or Fukushima, may also cause hypothyroidism.

With congenital hypothyroidism, newborns come into the world without a thyroid gland or with a partial thyroid gland.

Certain medications can also cause hypothyroidism (drug-induced hypothyroidism).

While this is not a comprehensive list, some of the more commonly known medications to have this effect include:

  • Lithium
  • Amiodarone
  • Interferon alpha
  • Interleukin-2

Hypothyroidism can also occur with too little iodine consumption (called iodine-deficiency hypothyroidism) or if too much iodine is consumed (called iodine-induced hypothyroidism).

In secondary or central hypothyroidism, the pituitary gland (located in your brain) is damaged from a tumor, radiation, or surgery and is unable to trigger the thyroid gland to produce thyroid hormone.

Rarely, hypothyroidism from infiltrative diseases (for example, sarcoidosis or hemochromatosis) can deposit substances (like granulomas or iron, respectively) into the thyroid gland, reducing its ability to function.


The diagnosis of hypothyroidism is made based on clinical examination and blood tests.

Clinical Examination

In addition to a clinical thyroid examination, which includes a manual and visual examination of the thyroid gland, a doctor will also perform a physical examination to look for signs of hypothyroidism.

Signs of hypothyroidism include dry, coarse skin, a slow heart rate, slow reflexes, and swelling.

Blood Tests

The main blood test used to diagnose hypothyroidism is the thyroid stimulating hormone (TSH) test. This test measures TSH, a pituitary hormone. TSH rises when it detects low levels of thyroid hormone and drops when it detects excess thyroid hormone.

Laboratories each have established a reference range, and levels above the reference range are considered potentially indicative of hypothyroidism.

In addition, the unbound and available levels of the actual circulating thyroid hormones—free thyroxine (free T4) and free triiodothyronine (free T3)—may be measured.

There are reference ranges for these two hormone tests, and levels below these ranges (showing that there is insufficient free T4 and/or free T3) are considered indicative of hypothyroidism.


Hypothyroidism is treated with a thyroid hormone replacement drug, which is a medication that replaces the missing thyroid hormone in the body.


The most commonly prescribed thyroid hormone replacement drug is known generically as levothyroxine, a synthetic form of the thyroid hormone thyroxine (T4).


There is also a synthetic form of the T3 hormone, known as liothyronine. It is sometimes added to levothyroxine as part of a therapy known as the T4/T3 combination treatment, though this practice is considered controversial by many endocrinologists and mainstream practitioners.

The official guidelines of various endocrinology organizations position levothyroxine as the preferred treatment and discourage T4/T3 combination therapy, as well as the use of natural desiccated thyroid.

Natural Desiccated Thyroid

Finally, there is a hormone replacement drug called natural desiccated thyroid, sometimes abbreviated NDT or called "thyroid extract." NDT contains natural forms of both T4 and T3.

While it has been available for more than a century and is still in use today, it is considered controversial by the mainstream medical community and is prescribed more often by integrative, functional, and holistic physicians, as compared to endocrinologists and conventional physicians.


Living well with hypothyroidism is not just about medication. It's also important to eat well to optimize both your thyroid and overall health. Figuring out exactly what to nourish your body with (and what to avoid putting in your body) can be tricky, however.

A Few "Eat Right" Tips

  • If you are trying to lose weight, consider starting a calorie restriction diet or the Zone Diet (under the guidance of your doctor or nutritionist).
  • Get certain vitamin (and mineral) levels checked (for example, vitamin D, vitamin B12, and selenium), as deficiencies in these substances may be more common in people with autoimmune thyroid disease.

In the end, while it may feel like you’re fighting an uphill battle with your diet, don't give up. You will eventually find the right strategy that will help you live and feel well.


Coping with hypothyroidism can be challenging, especially as you manage the intricacies of finding the right doctor, managing your thyroid medication, and simply figuring out how to fit this diagnosis (new or old) into your current life.

While burdensome at times, with acknowledgment of your emotions, support from loved ones, healthy lifestyle habits, and stress management, you can live well with this condition.

A Word From Verywell

In the end, whether you (or a loved one) has been recently diagnosed with hypothyroidism, or you are being currently treated for it and still not feeling right, please know that you are not alone. Continue to seek knowledge about your thyroid disease and remain resilient as you navigate this sometimes taxing journey.

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Article Sources
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