Hypothyroidism, which occurs when an underactive thyroid does not produce enough hormones, can be a dangerous condition if untreated.

Instead of the bodily systems speeding up and overheating, they slow down in a variety of ways. This thyroid disease's symptoms include the following:

  • Fatigue
  • Mental depression
  • Sluggishness
  • Feeling cold
  • Weight gain
  • Dry skin and hair
  • Constipation
  • Menstrual irregularities
Myxedema Coma

If you have severe hypothyroidism, a significant injury, infection, or exposure to cold or certain medications may trigger a life-threatening condition called myxedema coma. This condition may cause you to lose consciousness and to develop hypothermia, a life-threatening low body temperature.

Causes of Hypothyroidism

Hashimoto’s disease is the most common cause of hypothyroidism in the United States. It occurs when the immune system produces antibodies that attack the thyroid gland, creating chronic inflammation that damages the gland and interferes with its ability to make enough thyroid hormone. It occurs more often in women than men, and tends to run in families.

Hypothyroidism can be traced to several other conditions as well, including

  • Subacute, lymphocytic, or postpartum thyroiditis.  These inflammations of the thyroid gland often start as hyperthyroidism, as stored thyroid hormone leaks out of the gland and raises hormone levels in the blood. Most people then develop hypothyroidism before the thyroid is completely healed.  Rarely, this type of hypothyroidism is permanent.
  • Drugs that affect thyroid function, such as amiodarone, which is used to treat heart rhythm abnormalities.
  • A pituitary gland that does not make enough thyroid-stimulating hormone (TSH)
  • Treatment for hyperthyroidism (too much thyroid hormone) with radioactive iodine or surgery.

Routine testing of babies at birth identifies any with congenital hypothyroidism, a condition in which the thyroid gland has not developed properly. This testing is essential, because if hypothyroidism is not treated, a child could have mental slowness or retardation, or fail to grow normally.  Hypothyroidism during pregnancy can also negatively affect the baby. 

Hypothyroidism is increasingly common as we age. Women over 50 should consider being screened for thyroid deficiency every few years. Hypothyroidism affects as many as 15 percent of women over 70 years of age.

Hypothyroidism Treatment

Hypothyroidism is treated by replacing the thyroid hormone the body needs. This is usually done with an oral tablet or pill of the thyroid hormone thyroxine (T4 or levothyroxine). A person will usually notice an improvement in his or her health and decreased symptoms of thyroid disease within two weeks. Severe cases of hypothyroidism, however, may take longer to correct.

Most people with hypothyroidism will need to be on T4 treatment for the rest of their lives. They have to work closely with their doctor, take their medication as directed, and be monitored regularly in case the medication dose needs to be adjusted. If people take too much T4, they can develop a mild case of hyperthyroidism. If they do not get enough, the symptoms of hypothyroidism will return.

Some people with hypothyroidism may need special attention if he or she is

  • Older or has a weak heart. Thyroid hormone can make the heart work harder. A lower dose may be needed.
  • Pregnant. Higher doses may be needed during pregnancy. An adjustment in dosage may be necessary after delivering the baby as well.
  • Having surgery. A person having surgery should have enough T4 in his or her system to undergo the anesthesia and have a good recovery. If an individual is unable to take medicine by mouth, T4 can be given intravenously after surgery.


Leonard Wartofsky, MD, MACP
Washington Hospital Center
Georgetown University School of Medicine

Bryan Haugen, MD
University of Colorado Denver School of Medicine

Last Review: May 2013