There are many causes of hypothyroidism, such as thyroiditis, use of medications, and surgery. 1. Thyroiditis: Thyroiditis may lead to destruction of a large number of thyroid follicular cells or the production of autoantibodies against the thyroid gland, thus causing hypothyroidism. 2. Use of medication: For example, overdose of medication during the treatment of hyperthyroidism or damage to the thyroid gland after iodine-131 treatment may lead to the development of hypothyroidism. 3. Surgery: For example, too much of the thyroid gland is removed during thyroid surgery, resulting in hypothyroidism. If hypothyroidism occurs, it is recommended that the patient should consult a regular hospital, improve the examination, clarify the cause and deal with it actively.