Iodine-131 is an artificial radionuclide, which is relatively safe for the treatment of thyroid disorders. However, due to the presence of certain radiation, although it basically has no effect on tissues other than the thyroid gland, it may cause hypothyroidism, worsening of proptosis, hyperthyroidism crisis and other injuries: 1. Hyperthyroidism or thyroid cancer, the dosage is generally high, so about 70% of patients will suffer from hypothyroidism within 2 years of treatment. 2. Proptosis worsens: Some patients with proptosis may have their proptosis worsen after treatment. 3. This may cause hyperthyroidism crisis, which is relatively rare. Patients who are at risk of hyperthyroidism should be treated with anti-thyroid medication for about one month before treatment with iodine-131 to reduce the risk of hyperthyroidism. Iodine-131 therapy has certain advantages over anti-thyroid medication because it is a precise and targeted therapy with a low recurrence rate.