The reason why 131 iodine can treat hyperthyroidism is that most of the 131 iodine is absorbed by the thyroid gland after it enters the body and accumulates in the thyroid gland, and the 131 iodine releases beta rays during the decay process. This ray has a range of only a few millimeters in the thyroid gland, and the energy it releases can destroy hyperfunctional thyroid tissue and shrink the enlarged thyroid gland. Generally speaking, through 131 iodine treatment, more than 90% of patients with hyperthyroidism symptoms and signs can be quickly controlled and cured. Indications for 131 iodine treatment of hyperthyroidism: 1. Age above 25 years old, with moderate hyperthyroidism. 2.Anti-hyperthyroidism drugs have allergy and can not be used, or long-term treatment is ineffective, or relapse after treatment. 3.Combined heart, liver, kidney and other diseases that are not suitable for surgery, or recurrence after surgery, or those who are unwilling to operate. 4, Autonomous high-functioning nodular hyperthyroidism. According to the relevant literature, no matter what kind of hyperthyroidism treatment and non-treatment of the ultimate tendency to hypothyroidism, only hyperthyroidism will be combined with a serious impact on the health of the disease and even threaten the life, and the development of hypothyroidism is not interrupted. Therefore, hypothyroidism is not unique to radioisotope 131 iodine treatment. Hypothyroidism is characterized by a fear of cold, low perspiration, dry skin, swelling, tight skin, loss of appetite, bloating, constipation, inflexible joints, muscle aches, drowsiness, and poor mental performance. The diagnosis of hypothyroidism is very accurate and reliable by measuring thyroid hormones (FT3, FT4, sTSH). In the case of hyperthyroidism treated with 131 iodine, the incidence of permanent hypothyroidism has been reported to increase by 1-3% per year, with less correlation with the dose of radiopharmaceuticals given, and the greatest correlation with the patient’s sensitivity to the medication or autoimmune response. Once hypothyroidism occurs, it is important to have regular checkups in order to keep track of the dose of alternative medicine. Replacement therapy is simple, safe, cost-effective and has no side effects. Iodine-131 treatment for hyperthyroidism is safe, simple, cost-effective and effective, and basically can be cured with one dose of the drug.