The thyroid is a butterfly-shaped gland that lies in front of the windpipe (trachea) and just below the voice box (larynx). It makes hormones that regulate the way the body uses energy. The thyroid uses iodine from food to make 2 thyroid hormones, thyroxin (T4) and triiodothyronine (T3).

The thyroid gland stores these hormones and releases them into the blood stream as they are needed. If the thyroid does not produce enough hormones it is hypothyroidism and an overproduction of hormones causes hyperthyroidism.