Radioisotope is an effective treatment for hyperthyroidism, known as “internal medicine surgery without surgery”, widely recommended and accepted by doctors and patients in Europe and the U.S. 131I is an isotope of iodine, which can be ingested by the thyroid follicles, and 131I releases β-rays during the decay process, which has the ability to ionize the radiation and make the thyroid follicle cells degenerate and necrotic, thus reducing the synthesis and secretion of thyroid hormones and the volume of the thyroid is reduced. It has the ability of ionizing radiation to cause degeneration and necrosis of the thyroid follicle cells, thus reducing the synthesis and secretion of thyroid hormones, and the volume of the thyroid gland is also reduced, and ultimately achieve the purpose of treating hyperthyroidism. Some people may worry about the harm of 131I to the human body, in fact, it is less distributed in the tissues outside the thyroid gland and has a short retention time, so the amount of radiation produced on the human body is very low and is within the safe range. 131I treatment is usually effective in 2-3 weeks, with symptomatic relief, shrinkage of the thyroid gland and weight gain. The cure rate for a course of treatment is 52.6% to 77.0%, with an effective rate of over 95%. The possible most common adverse reaction is hypothyroidism, which requires lifelong application of thyroid hormone replacement therapy. So, who is it indicated for? Patients who are allergic to antithyroid drugs and experience other adverse reactions (such as liver and kidney impairment, leukopenia, etc.); patients with contraindications to surgery or high risk of surgery; and patients with combined heart disease can be treated with 131I.