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The thyroid gland is located inside the neck, just below your Adam’s apple. It produces two thyroid hormones, triiodothyronine (T3) and thyroxine (T4), which regulate how the body uses and stores energy. This is sometimes called your “metabolism.”


How well the thyroid works is controlled by another gland called the pituitary, which is located in your brain.

The pituitary produces thyroid-stimulating hormone (TSH), which stimulates the thyroid to produce T3 and T4.



Hypothyroidism means you have too little thyroid hormone. Another term is an “under-active thyroid.” Hypothyroidism is the most common thyroid disorder. It occurs more often in

women, it increases with age, and it runs in families. Symptoms include:

  • Tiredness
  • Mental depression
  • Sluggishness
  • Feeling cold
  • Weight gain (only 5–10 pounds)
  • Dry skin and hair
  • Constipation
  • Menstrual irregularities

These symptoms are not unique to hypothyroidism, and many people who are hypothyroid only have one or two of these symptoms. Luckily, a simple blood test can discover the condition early.



In adults, Hashimoto’s disease is the most common cause of hypothyroidism. This is a condition in which your immune system attacks your thyroid, so that it is damaged and can’t make enough hormones.

Hypothyroidism can also be caused by treatment with radioactive iodine or surgery on the thyroid gland (which are used to treat other types of thyroid disorders). A problem with the pituitary gland is another rare cause. Hypothyroidism can also be present from birth if the thyroid gland does not

develop properly.




In adults, untreated hypothyroidism leads to poor mental and physical performance, and can cause high blood cholesterol levels that can lead to heart disease. Also, a life-threatening condition called myxedema coma can develop with severe untreated hypothyroidism.

Diagnosis of hypothyroidism is especially important in pregnancy to ensure delivery of a healthy baby. Routine testing of all babies at birth identifies those with hypothyroidism. If not treated, a child could have mental slowness, retardation, or fail to grow normally.




Blood tests can measure your levels of thyroid-stimulating hormone (TSH) and thyroid hormone (T4). You have hypothyroidism when you have high TSH and low T4 levels in your blood. In very early or mild hypothyroidism, the TSH level will increase above normal level before the T4 drops below normal. Of the two blood tests, TSH is more important. Your doctor will pay more attention to TSH levels to make a diagnosis.

When the cause of hypothyroidism is Hashimoto’s disease, anti-thyroid antibodies that attack the thyroid can also be measured in the bloodstream.



Hypothyroidism is treated with thyroid hormone medication. Levothyroxine is the drug of choice. It is a synthetic (laboratorymade) form of T4 that is the same as the T4 the thyroid naturally makes. Not all thyroid hormone medicines are the same. If possible, you should stay with the same brand.

Thyroid hormone replacement is usually needed for life. If for any reason the medicine needs to be changed, it is important to have blood tests for TSH done again. Your dose will be adjusted based upon your TSH tests. Over time, doses of thyroid hormone that are too high can lead to bone loss, abnormal heart function, and abnormal heart rhythms. Doses that are too low may not relieve your symptoms.

Dose adjustment may be necessary during pregnancy and at other times, and can be discussed during your regular check-ups with your doctor.



If you have hypothyroidism, you need treatment. Otherwise, it could become a serious health problem.

If you have one or more of the symptoms of hypothyroidism, or if thyroid disease runs in your family, you should ask your doctor for a blood test. If the test is positive, you should tell your blood relatives about your condition. They too should have tests for thyroid disease.

Some experts also recommend checking thyroid function in early pregnancy and in all women over the age of 60, even if they don’t have symptoms.