What is hypothyroidism? Hypothyroidism is a common disorder that occurs when the thyroid gland is underactive and does not produce enough thyroid hormone. The thyroid gland is located in the front part of the neck, and it releases hormones that regulate your metabolism and how you use energy. The lack of thyroid hormone due to hypothyroidism slows the body’s chemical processes and metabolism. This leads to symptoms such as fatigue and weight gain. Hypothyroidism, also called myxedema, hypothyroid, or underactive thyroid, is more common in women than in men. It is also more common in people older than 50 years of age. Hypothyroidism is not curable, but it is treatable. Left untreated, hypothyroidism may lead to serious, potentially life-threatening complications, such as heart disease and rarely, myxedema coma. Seek prompt medical care if you have symptoms of hypothyroidism, such as cold hands and feet, fatigue, and weight gain. Timely diagnosis and treatment of hypothyroidism reduces the risk of serious complications.