Hypothyroidism (Underactive Thyroid)

Written by Kelli Miller, Liz Seegert
Medically Reviewed by Jabeen Begum, MD on January 13, 2025
10 min read

Hypothyroidism, also called underactive thyroid disease, is a condition in which your thyroid gland does not make enough thyroid hormone. Your thyroid gland is located in the front lower part of your neck. It releases hormones that travel through your bloodstream and affect nearly every part of your body, from your heart and brain to your muscles and skin.

Your thyroid controls how your body's cells use energy from food, a process called metabolism. Among other things, your metabolism affects your body’s temperature, your heartbeat, and how well you burn calories. If you don't have enough thyroid hormone, your body processes slow down. That means your body makes less energy, and your metabolism becomes sluggish.

Subclinical hypothyroidism

You may be diagnosed with subclinical hypothyroidism, also known as mild thyroid failure, if your levels of the hormone thyroxine (T4) are normal but your thyroid-stimulating hormone (TSH) levels are high. This means you don’t actually have hypothyroidism but are at a higher risk of developing the condition. 

About 3%-20% of people may develop subclinical hypothyroidism. You may be more likely to develop if you’re a woman or person assigned female at birth (AFAB), over 60, or have type 2 diabetes. You may not have symptoms and may not need treatment, but your doctor will want to monitor your thyroid levels regularly.

Hypothyroidism vs. hyperthyroidism

Unlike hypothyroidism, hyperthyroidism (overactive thyroid) happens when your thyroid gland makestoo much thyroid hormone, causing many of your body’s functions to speed up. You might lose weight (even if you’re hungrier than usual), your heart may beat faster or unevenly, your hands may shake, or your muscles may become weaker. You may feel more nervous or irritable, have problems sleeping, feel more tired, sweat more, or notice a lump in your neck, called a goiter.

Symptoms of hypothyroidism may be vague and can often mimic other conditions. They may include:

  • Changes in the menstrual cycle
  • Constipation
  • Depression
  • Dry hair and hair loss
  • Dry skin
  • Fatigue
  • Greater sensitivity to cold
  • Hoarse voice
  • Joint pain, stiffness, and swelling
  • Problems with memory
  • Muscle aches and stiffness
  • Muscle weakness
  • Puffy face
  • Slow heart rate
  • Swelling of the thyroid gland (goiter)
  • Unexplained weight gain or difficulty losing weight

Children and teens with hypothyroidism may also have the same symptoms as adults, along with:

  • Delays in puberty
  • Delays in growth 
  • Slow mental development
  • Slower development of permanent teeth

Babies with hypothyroidism may have no symptoms. If symptoms do occur, they can include:

  • Constipation
  • Hoarse cry
  • Little or no growth
  • Low muscle tone
  • Jaundice (yellowing of the skin and whites of the eyes)
  • Poor feeding habits
  • Puffy face
  • Stomach bloating
  • Swollen tongue
  • Umbilical hernia (a bulge near the navel)

Make an appointment with your health care provider if you or your baby has any signs of hypothyroidism. It’s important to note that these symptoms can be due to other medical conditions.

The most common cause of hypothyroidism is Hashimoto's disease — an autoimmune disorder that causes inflammation of the thyroid gland. With Hashimoto’s, your body produces antibodies that attack and destroy the thyroid gland.

Other causes include:

Radiation therapy to the neck area. Treating certain cancers, such as lymphoma, requires radiation to the neck. Radiation damages the cells in the thyroid. This makes it more difficult for the gland to produce hormones.

Use of certain medications. Certain medicines for heart problems, psychiatric conditions, and cancer can sometimes affect the production of thyroid hormone. These include amiodarone (Cordarone, Pacerone), interferon alpha, and interleukin-2.

Thyroid surgery. Surgery to remove the thyroid will lead to hypothyroidism. If only part of the thyroid is removed, the remaining gland may still be able to produce enough hormone for the body's needs.

Too little iodine in the diet. The thyroid needs iodine to produce thyroid hormone. Your body doesn't make iodine, so you need to get it through your diet. Iodized table salt is rich in iodine. Other food sources of iodine include shellfish, saltwater fish, eggs, dairy products, and seaweed. Iodine deficiency is rare in the U.S.

Pregnancy. The reason isn’t clear, but sometimes, inflammation of the thyroid occurs after pregnancy. This is called postpartum thyroiditis. People with this condition usually have a severe increase in thyroid hormone levels followed by a sharp drop in thyroid hormone production. Most people with postpartum thyroiditis will regain their normal thyroid function.

Problems with the thyroid at birth. Some babies may be born with a thyroid gland that does not develop or work properly. This type of hypothyroidism is called congenital hypothyroidism. Most hospitals in the U.S. screen babies at birth for this disease.

Pituitary gland damage or disorder. Rarely, a problem with the pituitary gland can interfere with the production of thyroid hormone. The pituitary gland makes a hormone, called thyroid-stimulating hormone (TSH), which tells your thyroid how much hormone it should make and release.

Primary vs. secondary hypothyroidism 

Primary hypothyroidism is caused by a problem with the thyroid gland itself. Secondary hypothyroidism occurs when another problem interferes with the thyroid's ability to produce hormones. For example, any problem with the pituitary gland or hypothalamus can make your thyroid underactive, as these glands produce hormones that trigger the release of thyroid hormone.

Sometimes, an underactive thyroid that results from a problem with the hypothalamus is called tertiary hypothyroidism.

Women and people assigned female at birth (AFAB), particularly older ones, are more likely to develop hypothyroidism than men. You are also more likely to develop hypothyroidism if you have a close family member with an autoimmune disease. Other risk factors include:

  • Having radiation therapy on your neck or chest
  • Recently being pregnant
  • Autoimmune disorders, such as type 1 diabetes or celiac disease
  • Having previous thyroid surgery or treatment for hypothyroidism

If you have symptoms of hypothyroidism, your doctor will order blood tests to check hormone levels. These may include:

Thyroid-stimulating hormone (TSH) blood test. Itmeasures your thyroid-stimulating hormone. This is usually the first test most providers recommend. Your pituitary gland makes TSH, which travels to your thyroid gland, prompting it to produce thyroid hormones, T3 and T4.

T4 (thyroxine) blood test. It measures how much of the thyroid hormone thyroxine (T4) the thyroid gland makes. If you have very low T4 levels, you probably have hypothyroidism. If your test results are not in the normal range, your doctor will do additional tests to find out why. Be sure to tell your doctor what medications you take, if you’re pregnant or are taking oral contraceptives, as they can interfere with T4 testing.

T3 (triiodothyronine, or free T3). It is a blood test that calculates the amount of triiodothyronine in your blood. This hormone is one of the two main hormones that your thyroid makes. Your doctor may check your T3 levels even if your T4 levels are normal, if they think you have hypothyroidism.

Thyroid antibody testing. This test looks for certain proteins in your blood. If thyroid antibodies are found, you may have an autoimmune condition, such as Hashimoto’s disease or Grave’s disease.

Thyroid ultrasound. It may be ordered if your blood tests or exam are abnormal, to look for inflammation or unusual swelling or nodules around your thyroid gland.

If you have hypothyroidism, your doctor will prescribe a synthetic (human-made) thyroid hormone called levothyroxine. You take this pill every day. Certain other medications can interfere with how your body absorbs this synthetic thyroid hormone. Make sure your doctor knows about all the medicines, herbs, and supplements you take, including over-the-counter products.

You will need regular blood tests to check your thyroid hormone levels. Your doctor may need to adjust your medication dose from time to time.

It can take a little time to figure out the correct dosage of thyroid hormone that you need. Your doctor will give you a blood test to check your TSH levels six to eight weeks after you start taking synthetic hormones, and then once every six months.

If your dosage is too high and you get too much hormone, you could have these side effects:

People with severe hypothyroidism or heart disease may start out with a low dose of synthetic hormone, and then gradually increase the amount so their heart can adjust to it.

Once you have the correct dosage, you shouldn’t have any side effects from your hormones. But don’t stop or skip your medication, as your hypothyroidism symptoms could come back.

If you gain or lose even as much as 10 pounds of body weight, you may need to get your TSH levels checked again to see if your hormone dosage should be adjusted.

Some natural treatments can help support overall health and overall well-being. Remedies such as ginger or carnitine may help with your symptoms, but they won’t increase thyroid hormones. Some treatments labeled as “natural” can actually be harmful, as herbs and other products can interfere with how other medicines work in your body. 

Your doctor may suggest taking supplements, such as iron, vitamin D, B12, or zinc, in certain situations. If you take levothyroxine for hypothyroidism, there is no need to take iodine supplements. There is very little proof that supplements affect how well your thyroid works, but they can help if you’re not getting enough of certain vitamins or minerals in your diet.

A natural treatment that shows some promise is desiccated thyroid extract. This is a thyroid hormone pill made from animal thyroid gland and is available with a prescription. In studies, people who took this medication had similar test results to people who took levothyroxine. But more research is needed before it can become more widely used. 

You may find that Integrative medicine — which uses a mind/body approach through practices such as yoga, meditation, or acupuncture — may help with medication side effects.

There’s no one “best” diet for hypothyroidism, but doctors suggest eating plenty of fruits, vegetables, lean protein and grains. Foods that are high in selenium, such as some fish, cottage cheese, and Brazil nuts, may help your thyroid work better. Be careful when eating certain foods, or eating them too close to the time you take your medication, as they can make your medications less effective:

  • Soy/soybean flour
  • Kelp
  • Walnuts
  • Cottonseed meal
  • Cruciferous vegetables 

Too much fiber in your diet can also keep your body from absorbing your medicine properly.

Cassava (yuca) is one root vegetable that doctors suggest avoiding if you have hypothyroidism. It can be dangerous if not properly prepared. 

Eating a balanced diet is the best way to make sure you get all the nutrients your body needs. Be sure to discuss a hypothyroid-friendly diet with your doctor before adding or eliminating any foods.

Untreated, hypothyroidism may cause complications, such as:

Balance problems. Older people are at extra risk for balance problems if their thyroid hormone levels are too low.

Goiter. If your thyroid is always trying to produce more hormones, the gland can swell and change the appearance of your neck. You may also have trouble swallowing.

Heart problems. Hypothyroidism puts you at a greater risk for heart disease and can raise your levels of LDL or “bad” cholesterol.

Infertility. Too little thyroid hormone may disrupt your production of eggs (ovulation) and make it harder to conceive.

Joint pain. Low levels of thyroid hormone can cause you to have aches and pains in your joints and muscles, as well as tendonitis.

Mental health issues. Low thyroid hormones can cause memory or concentration lapses, as well as decreased interest in activities you used to enjoy. See your doctor if you notice these changes, as they could also be due to depression unrelated to your thyroid.

Obesity. Although hypothyroidism may curb your appetite, you can gain weight because your metabolism slows down and you don’t burn enough calories.

Peripheral neuropathy. Over time, low thyroid hormones can damage your peripheral nerves. You may notice pain, tingling, or numbness in your limbs.

Thyroid problems in a pregnant woman can affect the developing baby. During the first three months of pregnancy, the baby receives all thyroid hormone from its mother. If the mother has hypothyroidism, the baby does not get enough thyroid hormone. This can lead to problems with mental development.

Extremely low levels of thyroid hormone can cause a life-threatening condition called myxedema — which is the most severe form of hypothyroidism. A person with myxedema can lose consciousness or go into a coma. The condition can also cause the body temperature to drop very low, which can cause death.

Hypothyroidism occurs when your thyroid gland makes too little thyroid hormone for your body’s energy needs. It is treatable with medication. If you’re having symptoms such as unexplained fatigue, weight gain or loss, trouble sleeping, irregular or slow heartbeat, muscle or joint pain or weakness, ask your doctor to test your thyroid levels, especially if you are pregnant, assigned female at birth (AFAB), or are over 60. Some changes to your diet and certain supplements may help with symptoms but can’t cure thyroid disease. Some remedies or foods may interfere with your medication. Talk with your doctor about your diet and lifestyle, and about any supplements, herbs, or alternative medicine you are considering.

What worsens hypothyroidism?

Eating foods with a lot of iodine — like kelp or other kinds of seaweed — can cause hypothyroidism or make the condition worse. So can taking iodine supplements or even cough syrup. If you are pregnant, it’s especially important to talk to your doctor about whether to take any iodine supplements, since your baby gets iodine from your diet.

How does hypothyroidism affect your life?

If you are diagnosed with hypothyroidism, you will need medication for the rest of your life, but otherwise, you can live normally. You will also need to be more aware of your diet, and avoid or cut back on certain foods, such as soy or kelp, especially around the time you take your medicine.

Can hypothyroidism be cured?

Right now, there is no cure for hypothyroidism. However, daily medication can help you live a normal life.