Endocrine System Home > Hypothyroidism

If a person's levels of thyroid hormone are abnormally low, it is called hypothyroidism. It is often directly related to conditions affecting the thyroid gland, but can also be caused by medications, surgery, or iodine deficiency. In the early stages, there may be no symptoms. Left untreated, a person may eventually experience weight gain, joint pain, and a puffy face. Medications are typically all that is needed to treat an underactive thyroid.

What Is Hypothyroidism?

Hypothyroidism (also known as an underactive thyroid) is when your thyroid does not make enough thyroid hormones to meet the body's needs. Without enough thyroid hormone, many of the body's functions slow down.
About 5 percent of the U.S. population has hypothyroidism. Older adults and women in general are much more likely to develop this condition. About 15 percent of older women have an underactive thyroid.

What Is the Thyroid Gland?

The thyroid is a two-inch-long, butterfly-shaped gland. It is located in the front of the neck below the larynx, or voice box, and above the clavicles (collarbones). It is made up of two lobes, one on either side of the windpipe.
The thyroid is one of a group of glands that are part of the endocrine system. The endocrine glands produce, store, and release hormones into the bloodstream that travel through the body and direct the activity of the body's cells. Thyroid hormones regulate metabolism, which is the way the body uses energy, and affect nearly every organ in the body.
The thyroid gland makes two thyroid hormones: triiodothyronine (T3) and thyroxine (T4). Thyroid hormones affect metabolism, brain development, breathing, heart and nervous system functions, body temperature, muscle strength, skin dryness, menstrual cycles, weight, and cholesterol levels.
Thyroid hormone production (both T3 and T4) is regulated by thyroid-stimulating hormone (TSH), which is made by the pituitary gland. Located in the brain, the pituitary gland is the "master gland" of the endocrine system.
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Last reviewed by: Arthur Schoenstadt, MD
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