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This topic provides information about hypothyroidism. Hypothyroidism means your thyroid is not making enough thyroid hormone. If you are looking for information about when the thyroid makes too much thyroid hormone, see the topic Hyperthyroidism.

What is hypothyroidism?

Hypothyroidism means your thyroid is not making enough thyroid hormone. The thyroid is a butterfly-shaped gland in the front of your neck. It makes hormones that control the way your body uses energy.

See a picture of the thyroid gland .

Having a low level of thyroid hormone affects your whole body. It can make you feel tired and weak. If hypothyroidism is not treated, it can raise your cholesterol levels and make you more likely to have a heart attack or stroke. During pregnancy, untreated hypothyroidism can harm your baby. Luckily, hypothyroidism is easy to treat.

People of any age can get hypothyroidism, but older adults are more likely to get it. Women age 60 and older have the highest risk. You are more likely to get the disease if it runs in your family.

What causes hypothyroidism?

In the United States, the most common cause is Hashimoto's thyroiditis. It causes the body’s immune system to attack thyroid tissue. As a result, the gland can't make enough thyroid hormone.

Other things that can lead to low levels of thyroid hormone include surgery to remove the thyroid gland and radiation therapy for cancer. Less common causes include viral infections and some drugs, such as lithium.

What are the symptoms?

Hypothyroidism can cause many different symptoms, such as:

• Feeling tired, weak, or depressed.
• Dry skin and brittle nails.
• Not being able to stand the cold.
• Constipation.
• Memory problems or having trouble thinking clearly.
• Heavy or irregular menstrual periods.

Symptoms occur slowly over time. At first you might not notice them, or you might mistake them for normal aging. See your doctor if you have symptoms like these that get worse or won't go away.

How is hypothyroidism diagnosed?

Your doctor will ask questions about your symptoms. You will also have a physical exam. If your doctor thinks you have hypothyroidism, a simple blood test can show if your thyroid hormone level is too low.

How is it treated?

Doctors usually prescribe thyroid hormone pills to treat hypothyroidism. Most people start to feel better within a week or two. Your symptoms will probably go away within a few months. But you will likely need to keep taking the pills for the rest of your life.

It's important to take your medicine just the way your doctor tells you to. You will also need to see your doctor for follow-up visits to make sure you have the right dose. Getting too much or too little thyroid hormone can cause problems.