Most common cause of hypothyroidism is an autoimmune disease where the body's immune system attacks the thyroid gland, causing inflammation, also called Hashimoto's thyroiditis. Other causes include:treatment for hyperthyroidism(an overactive thyroid), radiation therapy for cancer, thyroid surgery and certain medications used to treat certain psychiatric disorders. Other rare causes include:iodine deficiency, abnormal thyroid development in babies and a pituitary gland problem.
Attribution: Straight Talk Foundation