Hypothyroidism is an underactive thyroid gland. Hypothyroidism means that the thyroid gland can’t make enough thyroid hormone to keep the body running normally. People are hypothyroid if they have too little thyroid hormone in the blood. Common causes are autoimmune disease, surgical removal of the thyroid, and radiation treatment.

Symptoms. Hypothyroidism doesn’t have any characteristic symptoms. There are some symptoms which might relate to hypothyroidism and many symptoms of hypothyroidism can occur in people with other diseases. One way to help figure out whether your symptoms are due to hypothyroidism is to think about whether you’ve always had the symptom (hypothyroidism is less likely) or whether the symptom is a change from the way you used to feel (hypothyroidism is more likely).