The thyroid is a butterfly-shaped gland that lies in front of the windpipe, also known as the trachea, and just below the voice box, also called the larynx. This gland makes hormones that regulate the way the body uses energy.

The thyroid gland uses iodine from food to make two thyroid hormones: thyroxine (T4) and triiodothyronine (T3). The thyroid gland stores these hormones and releases them into the bloodstream as they are needed.

If the thyroid gland does not produce enough hormones, it is called hypothyroidism. If the gland produces too many hormones, it is called hyperthyroidism. Problems with the thyroid gland can affect many body systems. Changes in weight, heartbeat, body temperature, digestion, and muscle function are common. Both hypothyroidism and hyperthyroidism can be treated, usually with medicine and sometimes with surgery.