What Is Hypothyroidism?

Hypothyroidism—or underactive thyroid—is a condition that occurs when your thyroid gland does not make enough thyroid hormone. The thyroid gland is a butterfly-shaped organ located in the neck, which plays an important role in regulating your hormones, metabolism, and body temperature.

Having an underlying autoimmune disease, taking certain medications, and undergoing radiation are some causes of hypothyroidism. Historically, about 5% of people in the U.S. have received a diagnosis for an underactive thyroid. However, a 2023 study reported that the number of people with hypothyroidism is increasing and researchers estimate that 11.4% of people had this condition in 2019.

While there is no cure for hypothyroidism, the good news is that you can treat the condition with medications that can help you restore your hormone levels and thyroid function.


Your hypothyroidism symptoms can vary in severity. Some people may also experience just a few of the following symptoms, while others have most symptoms. Generally, symptoms reflect a slowing down of metabolism and energy in the body.

Common symptoms of hypothyroidism include:

  • Goiter (or, an enlarged thyroid)
  • Fatigue
  • Hair loss
  • Unintentional weight gain
  • Difficulty losing weight
  • Slow heart rate
  • Trouble sleeping
  • Irritability or depressed mood
  • Slow movement or speech
  • Feeling cold
  • Pale, cool, or dry skin
  • Constipation
  • Having trouble sweating
  • Heavy and irregular menstrual periods
  • Experiencing difficulties getting pregnant
  • Brittle nails
  • Joint pain
  • Swollen or puffy face

When to Seek Medical Attention

If you suspect you have an underactive thyroid or are experiencing hypothyroidism symptoms, it's a good idea to get tested as soon as you can. While early detection can help you get started on treatment sooner, it can also prevent serious complications such as myxedema coma—a medical emergency that occurs when you have severely low thyroid hormone. Going into a myxedema coma can be fatal.



There are many possible causes of hypothyroidism. The endocrine system (or, the system in your body that controls hormones) includes many glands and organs that influence one another to keep the body functioning. Any imbalance in the system can affect the way hormones are made and released. These imbalances may occur for any one of the following reasons.

Autoimmune Disease

For unknown reasons, the immune system can sometimes mistakenly attack normal, healthy body tissues. When this happens to the thyroid gland it is called autoimmune thyroiditis. One type of autoimmune thyroid disease is Hashimoto's disease.

The immune system can attack healthy cells slowly over time or rapidly harm your thyroid gland. If you have Hashimoto's disease, your cells can quickly become damaged, making it difficult for your thyroid to make enough hormones to support your metabolism and energy.

Medical Procedures

In some cases or due to an underlying injury or condition, you might need surgery to remove some or all of the thyroid gland. As a result, your body might have trouble producing thyroid hormone which can cause an underactive thyroid. Thyroid cancer and overactive thyroid are two of many reasons you may need this kind of surgery.

If you have any head or neck cancers near your thyroid, your provider will likely recommend radiation therapy for treatment. Getting radiation on or near your thyroid gland can reduce your thyroid's ability to function and result in the onset of hypothyroidism symptoms.

Congenital Thyroid Conditions

Some babies have congenital hypothyroidism—or, a condition where they are either born without a working thyroid, have a thyroid that does not work properly, or the thyroid developed in the wrong place. Most of the time, this condition is chronic (life-long) and requires treatment throughout the life span to manage symptoms.


Some medications that are used to other medical conditions can cause hypothyroidism as a side effect. Medications that can cause underactive thyroid include:

  • Nexterone (amiodarone): Treatment for heart conditions
  • Priadel (lithium): Medication for bipolar disorder
  • Intron A (interferon alpha): Used for various cancers and tumors
  • Proleukin (interleukin-2): Helps treat some cancers

There are other medications that can potentially cause hypothyroidism, so it's important to check with your provider if you're noticing symptoms of underactive thyroid after use.

Iodine Levels

Iodine is a mineral that is found in some of the foods we eat and is commonly added to table salt. Your thyroid requires a proper amount of iodine to make thyroid hormones. However, too much or too little iodine can lead to thyroid disorders.

Pituitary Gland Problems

The pituitary gland is the primary gland that helps regulate your endocrine system. If your pituitary gland is damaged or not working correctly, it fails to send the correct signals to the thyroid gland which can make it difficult for your thyroid to function as normal, causing hypothyroidism symptoms.

Risk Factors

Anyone can have hypothyroidism, but some people may be at increased risk of developing the condition. You might have a higher likelihood of experiencing symptoms if you:

  • Were assigned female at birth
  • Are over the age of 60
  • Previously had thyroid surgery
  • Received radiation treatment
  • Have a family history of thyroid disease
  • Recently gave birth


Your healthcare provider can use a variety of exams to diagnose you with an underactive thyroid. These measures include:

  • Physical exam and medical history: Asks about your personal and family health history, learns about your symptoms, and examines your neck and body for changes
  • Blood tests: Uses lab testing to check your hormone levels (such as TSH and T4)
  • Imaging tests: Takes picture of your neck to look for thyroid nodules, an enlarged thyroid, or other concerns

TSH Levels

The most common blood test to check your thyroid function is a TSH (thyroid stimulating hormone) test. A lab technician can will collect a small amount of blood from your vein and measure the sample in a lab. High TSH levels indicate a low-functioning thyroid gland.


Unfortunately, there is no cure for hypothyroidism at this time. Treatments focus on using medication to replace the lack of hormones in your thyroid. This helps your body restore metabolism, temperature, and energy levels. Treatments are generally the same for everyone with an underactive thyroid no matter what originally caused the thyroid to malfunction.

The generic name for a very common thyroid medication is Synthroid (levothyroxine), which is a pill that you take first thing in the morning about an hour before eating. Most people need to take this medication daily for the rest of their lives. Your provider will generally order regular blood tests to monitor your thyroid hormone levels in the blood.

Some researchers are studying levothyroxine in combination with other medications to see if those treatments are more effective. And, there are ongoing studies to best understand when to start treatment for low thyroid levels. If you have questions or concerns, but sure to speak with your provider about your health situation.

How to Prevent Hypothyroidism 

Unfortunately, there are no ways to prevent hypothyroidism. For the general population, blood tests to screen for low thyroid levels are not recommended for people without symptoms. If you have a condition that increases your risk for hypothyroidism (a family history of thyroid issues, thyroid cancer, radiation therapy to the neck, or neck surgery), your provider may recommend yearly blood tests.

If you don't have a history of thyroid problems, but begin to experience symptoms, talk to your provider about getting tested.

Related Conditions

If you have hypothyroidism, you may be more likely to also receive a diagnosis for other health conditions. Similarly, other health conditions may also cause an underactive thyroid. Conditions that commonly co-occur (or, happen at the same time) as hypothyroidism include:

Living With Hypothyroidism

While there is no cure for hypothyroidism, the good news is that you can manage the condition with medication. Getting a diagnosis of hypothyroidism can be a challenge and might lead to some changes in your lifestyle, but many people find they feel much better once they are receiving the correct dose of medication to treat the condition.

Keep in mind: continue to monitor yourself for symptoms of underactive thyroid hormone levels once you are stable on treatment. It's important to let all of your healthcare providers know about any changes to your health, body weight, or medications. Many people with hypothyroidism may also need to get blood tested each year to monitor hormone levels and adjust treatment, if necessary.

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8 Sources
Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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