The thyroid is a gland in the neck that produces hormones that help to regulate metabolism, the reactions that control how the body uses energy. Hyperthyroidism is a disease in which the thyroid makes too much thyroid hormone, speeding up many of the body's functions. Symptoms of hyperthyroidism include rapid heartbeat, feeling hot, anxiety, muscle weakness, frequent bowel movements, trouble sleeping, shakiness, light or missed menstrual periods, and weight loss. Hypothyroidism is a condition in which the thyroid makes too little thyroid hormone and body functions slow down. Symptoms of hypothyroidism include tiredness, feeling cold, constipation, hoarse voice, changes in hair and skin, heavy menstrual periods, and weight gain. Doctors diagnose thyroid disease by checking blood levels of thyroid hormones. Thyroid disease can usually be easily treated with drugs; radiation; or, occasionally, surgery. Thyroid disease is very common and not all patients develop symptoms, especially early in the course of the disease. Subclinical thyroid disease is a term that doctors use to describe people who have normal blood levels of thyroid hormones but abnormal levels of thyroid-stimulating hormone, which is made in the pituitary gland and regulates the thyroid gland. Doctors disagree about the need to treat subclinical thyroid disease. Some doctors think it helps patients to treat it, and others think it is best to wait until symptoms develop before starting treatment