It doesn’t say “can’t” be used, but “shouldn’t” be used. Then under what circumstances can it be used? Iodine 131 should be used only as a last resort. Iodine 131 is used to treat hyperthyroidism in children and adolescents in two main situations: first, when the side effects of antithyroid medications such as methimazole or PTU are too great to continue using them; and second, when the hyperthyroidism is very serious and surgery is not possible. Why should children not be treated with Iodine 131? The main concern is the long-term damage of Iodine 131. Firstly, Iodine 131 treatment will inevitably lead to hypothyroidism, which is almost irreversible and lifelong; secondly, the radiation may induce thyroid cancer or other malignant tumors; thirdly, it may affect the future growth and development of children, such as the development of the gonads, etc. However, there is no large sample study showing that Iodine 131 treatment is suitable for children with hyperthyroidism. However, there is no large sample study to show the significant difference between children with hyperthyroidism treated with iodine 131 and those not treated with iodine 131 when they reach adulthood. However, in view of the radiation hazard and for safety reasons, Iodine 131 treatment in children is generally not recommended unless it is absolutely necessary. Is there a specific age limit? There is no specific age limit, either in China or abroad. Even at the time the guidelines were developed, it was not clear whether Iodine 131 treatment could be given to children older than 15 or 18 years of age.