What is hyperthyroidism? Hyperthyroidism is a disease in which an overactive thyroid gland produces too much thyroid hormone. The thyroid gland is located in the front of the neck and produces a hormone critical to normal metabolism. When the thyroid gland produces too much thyroid hormone, it leads to overstimulation of the body’s metabolism. Typical symptoms include nervousness, anxiety, weight loss, and hypertension. Hyperthyroidism can be caused by a variety of factors, including an autoimmune response of the body or an abnormal growth on the thyroid gland. A condition called Graves’ disease is the most common cause of hyperthyroidism. Other causes include thyroid nodules, iodine-induced hyperthyroidism, and excessive levels of thyroid stimulating hormone from the pituitary gland. Hyperthyroidism is more common in women than in men. Prompt diagnosis and treatment of hyperthyroidism can lead to a good prognosis or a cure in some cases. With regular medical care and compliance with treatment plans, many people with the disease live active, normal lives. Hyperthyroidism can lead to serious, potentially life-threatening symptoms and complications, such as cardiac arrhythmias and heart failure. Seek immediate medical care (call 911) if you, or someone you are with, have symptoms such as chest pain, palpitations, or shortness of breath.