Hyperthyroidism (overactive thyroid) is a condition caused by too much thyroid hormone in the body. It is also known as thyrotoxicosis.

The thyroid gland is located in the front of the neck, just below the larynx (voice box). It helps to maintain a healthy metabolism (the process by which foods are transformed into basic elements which can be utilized by the body for energy or growth) by producing and releasing iodine-containing hormones called thyroxine (T4) and triiodothyronine (T3).

T4 helps...