What is an underactive thyroid condition?
With an underactive thyroid (hypothyroidism), the thyroid gland (located in the front of the neck) fails to produce enough of a substance called thyroid hormone. Thyroid hormone is important for almost every function that the body performs. When thyroid hormone is too low, all body functions slow down; when it is too high, body functions speed up. An underactive thyroid is treated with a daily pill that replaces thyroid hormone.