Hyperthyroidism is a medical condition. It is caused by a thyroid gland that is too active. The thyroid gland makes hormones. These hormones manage the body’s metabolism. An example of one of these hormones is thyroxine. The thyroid-stimulating hormone starts the making of thyroxine. The thyroid-stimulating hormone is also called “TSH.” TSH is made in the pituitary gland. Hyperthyroidism is determined by a doctor by blood tests that show a decreased thyroid-stimulating hormone (TSH) level.