131I therapy is a relatively safe treatment. To date, it has not been possible to determine the upper limit of 131I treatment dose (both single dose and cumulative dose) through prospective clinical studies. However, retrospective statistical analysis suggests that the risk of radiation side effects increases with the number of 131I treatments and the cumulative 131I dose. The more common side effects include chronic salivary gland injury, dental caries, nasolacrimal duct obstruction, or gastrointestinal reactions. 131I treatment rarely causes bone marrow suppression and renal function abnormalities, which can be detected promptly by monitoring blood and renal function before and after treatment. there is no consistent conclusion on the relationship between 131I treatment and secondary tumors. There is insufficient evidence that 131I treatment affects the reproductive system, but women are advised to avoid pregnancy for 6-12 months after 131I treatment.