Thyroid-stimulating hormone (TSH) is a pituitary hormone that regulates thyroid function in conjunction with thyrotropin-releasing hormone (TRH). Specifically, TSH induces production of Thyroxine (T4) which is converted triiodothyronine (T3) and is responsible for stimulating the metabolism. TSH is secreted throughout life but reaches high levels during the periods of rapid growth and development, as well as in response to stress.