What is hypothyroidism?

Hypothyroidism happens when a gland in your neck, called the thyroid gland, makes too little thyroid hormone. This hormone controls how the body uses and stores energy ( figure 1).
With a different condition, hyperthyroidism, the thyroid gland makes too much thyroid hormone. With hypothyroidism, it does not make enough. Doctors sometimes also use the term “underactive thyroid.”

What causes hypothyroidism?

Different things can cause the thyroid gland to be unable to make enough thyroid hormone. These include:

• Problems with the immune system – The immune system is the body’s infection-fighting system. Sometimes, a person’s immune system attacks healthy cells, such as cells in the thyroid. This is called “chronic autoimmune thyroiditis” or “Hashimoto’s thyroiditis.” It is the most common cause of hypothyroidism in the US.
  Thyroidectomy – This is surgery to remove the thyroid gland.
• Radioiodine therapy – This is a treatment used for hyperthyroidism. It often causes
  hypothyroidism because it destroys part of the thyroid gland.
• Radiation in the neck area – High doses of radiation (for example, to treat cancer) can damage the thyroid gland.
• Certain medicines

The treatment of hypothyroidism is the same no matter what caused it.

What are the symptoms of hypothyroidism?

Some people with hypothyroidism have no symptoms. But most people feel tired. That can make it hard to know if a person has it, because a lot of conditions can make you tired.
Other symptoms of hypothyroidism include:

• Lack of energy
• Getting cold easily
• Developing coarse or thin hair
• Getting constipated (having too few bowel movements)

If it is not treated, hypothyroidism can also weaken and slow your heart. This can make you feel out of breath or tired when you exercise. It can also cause swelling (fluid buildup) in your ankles. Untreated hypothyroidism can also increase your blood pressure and raise your cholesterol. Both of these things increase the risk of heart problems.

Hypothyroidism can disrupt monthly periods. It can also make it hard to get pregnant. In people who do get pregnant, hypothyroidism can cause problems. For instance, it can increase the chances of having a miscarriage. (A miscarriage is when a pregnancy ends on its own before 20 weeks.)

Is there a test for hypothyroidism?

Yes. Your doctor or nurse can check for hypothyroidism using a simple blood test.

How is hypothyroidism treated?

Treatment involves taking thyroid hormone pills every day. After you take the pills for about 6 weeks, your doctor or nurse will test your blood again. This is to make sure that the levels are where they should be. They might adjust your dose depending on the results. Most people with hypothyroidism need to keep taking thyroid pills for the rest of their life. This gives your body the right level of the hormone that it cannot make on its own.

Thyroid hormone pills come in different brand name and generic forms. All of the pills work equally well. If possible, stick with the same generic or brand name. But switching between pills does not cause problems for most people. Talk to your doctor or nurse if you want to switch for some reason.
Never change your dose of thyroid hormone on your own. Taking too much thyroid hormone can cause heart rhythm problems and even damage your bones.

What if I want to get pregnant?

You can try to get pregnant. Many people with hypothyroidism have healthy pregnancies. But your doctor or nurse will most likely need to change your dose of thyroid hormone once you are pregnant. That’s because you need more thyroid hormone during pregnancy. They will also measure your levels of thyroid hormone 4 weeks after any change in your dose, and at least once during each trimester of pregnancy.

Thyroid and parathyroid glands

The thyroid is a butterfly-shaped gland in the middle of the neck. It sits just below the larynx (voice box). The thyroid makes 2 hormones, called T3 and T4, which control how the body uses and stores energy. The parathyroid glands are 4 small glands behind the thyroid. They make a hormone called parathyroid hormone, which helps control the amount of calcium in the blood.