131 iodine refers to radioactive iodine 131, which is commonly used in the treatment of hyperthyroidism, ectopic thyroid and other diseases, and can also be used as an adjunctive therapeutic measure after thyroid cancer surgery. 1. Hyperthyroidism: the rays released by radioactive iodine 131 have a certain degree of radioactivity. It can be specifically ingested and absorbed by thyroid tissues, causing damage to thyroid cells and removing excess hyperthyroid tissues, and is commonly used in the treatment and diagnosis of hyperthyroidism. 2. Ectopic thyroid: For thyroid tissues found in other organs and tissues of the body, i.e. ectopic thyroid, radioactive iodine 131 can also be used to destroy thyroid tissues, so as to achieve therapeutic effect. 3. Postoperative adjuvant therapy for thyroid cancer: the radioactivity of iodine 131 can destroy the thyroid cancer cells that have not been removed cleanly, so it can be used as adjuvant therapy for thyroid cancer patients after surgery. Iodine 131 treatment is less harmful to the body than radiotherapy, but patients may have adverse reactions such as nausea and vomiting, fatigue and inhibition of blood system during the treatment, if the discomfort is serious, they should communicate with the attending doctor in time.