The optimal outcome of radioactive iodine treatment of hyperthyroidism is normalization of thyroid function without permanent hypothyroidism, but in practice this goal is difficult to achieve. Because, if the dose of radioactive iodine is reduced, it will often lead to treatment failure, and the patient will need to undergo radioactive iodine treatment again, or become chronic subclinical hyperthyroidism. So some foreign scholars feel that patients should be told to receive hypothyroidism as the end result of iodine treatment for Grave’s disease. And it has been well documented that there is no ideal dose for radioactive iodine therapy that can effectively correct hyperthyroidism without causing hypothyroidism. There are a variety of factors that can affect the final outcome of 131I therapy, including: the patient’s own characteristics (e.g., age, sex, thyroid weight, etc.); the severity and duration of autoimmune thyroid irritation; the degree of absorption of radioactive iodine by the gland (including: uptake rate of 131I, average distribution, effective half-life, etc.); and the duration of thyroid drug therapy. It is important to point out two facts: First, the higher the cure rate of hyperthyroidism, the greater the possibility of hypothyroidism; Second, some patients even if the use of a very small dose of radioactive iodine will still occur hypothyroidism. It is now recognized that 131I administration, whether by the fixed-dose method or by dose determination based on thyroid weight or radioactive iodine uptake rate, is an effective treatment for Grave’s hyperthyroidism and will result in hypothyroidism in some patients over time. Therefore, the American Thyroid Association’s 2005 Graves’ Disease Guidelines advise patients, “No matter how well your hyperthyroidism is controlled, you will someday become hypothyroid because hyperthyroidism itself has a tendency to progress to hypothyroidism, which may be due to the presence of a low level of inflammation in your own thyroid gland. If you have radioactive iodine therapy or surgery, hypothyroidism may occur faster, but even if you are treated only with antithyroid medication, hypothyroidism will still occur because hyperthyroidism itself tends to develop into hypothyroidism, and you will one day have hypothyroidism”.