Thyroxine is one of the most important hormones in the human body, and low thyroid hormone can easily cause hypothyroidism. The causes of low thyroid hormone are as follows: I. Autoimmune hypothyroidism, including chronic lymphatic thyroiditis, or idiopathic hypothyroidism. Second, medical hypothyroidism, such as drug radiotherapy or iodine surgery, can cause medical hypothyroidism. Endemic iodine deficiency, or hypothyroidism caused by iodine. Enzyme synthesis hypothyroidism. Congenital thyroid deficiency, or hypothyroidism. Symptoms include fatigue, loss of appetite, and overweight. Dull facial expression, unresponsiveness, constipation, chest tightness, shortness of breath, female amenorrhea, infertility, male impotence, dry and rough skin. It presents with recurrence of infections, depression, drooping eyes, dry and thinning hair. In particular, it can cause low heart sounds, arrhythmia, heart failure or pericardial effusion.