The side effects of iodine-131 treatment for hyperthyroidism are mainly radioactive thyroiditis, aggravation of proptosis, hypothyroidism and hyperthyroidism crisis in severe cases. 1. Radioactive thyroiditis: After iodine-131 treatment for hyperthyroidism, some patients are prone to radioactive thyroiditis and pain in the thyroid area within a short period of time. At the same time, due to the short-term increase in thyroid hormone levels, sympathetic excitement, elevated body temperature, cardiac insufficiency, and even serious gastrointestinal symptoms may occur. 2. Eye protrusion: After iodine-131 treatment for hyperthyroidism, some patients with thyroid-related eye disease may experience increased eye symptoms, with more protruding eyes, and some patients may experience increased activity. . In addition, the conjunctiva is prone to congestion and edema and co-infection; 3. Hypothyroidism: After iodine-131 treatment for hyperthyroidism, the thyroid function must be monitored regularly. This is because some patients are prone to hypothyroidism as time goes on, and the incidence of hypothyroidism will increase as the treatment time goes on. This is mainly due to the fact that after iodine-131 treatment, the thyroid tissue is damaged by beta rays and fibrosis is gradually aggravated. At this time, the synthesis and secretion of thyroid hormones by the thyroid gland will gradually decrease, and long-term oral medication is required. 4. Hyperthyroid crisis: As a large number of thyroid follicular cells are destroyed, thyroid hormones are released into the blood, which can easily lead to the occurrence of hyperthyroid crisis or aggravation of hyperthyroid symptoms. Therefore, for hyperthyroidism iodine-131 treatment, preoperative evaluation is needed to understand whether there are any relevant contraindications. It is usually an absolute contraindication for women who are pregnant or breastfeeding, and is recommended with caution for patients who are too young or have active proptosis, and for patients with intolerable hyperthyroid heart disease. Patients with some drug allergy to oral antithyroid drugs, or who suffer from granulocyte deficiency and hepatic impairment, are usually advised to opt for iodine-131 treatment if their bodies can tolerate it.