Swelling of the neck after drinking iodine 131 may be a normal phenomenon, usually without treatment, if more serious, you can consult a doctor to give symptomatic treatment. The principle of iodine 131 treatment for hyperthyroidism is that iodine 131 releases beta rays in the process of decay, and beta rays have strong ionizing radiation ability, which makes part of the thyroid follicular cell degeneration and necrosis, and reduces the synthesis and secretion of thyroid hormones, and then reduces the volume of the thyroid gland, which achieves the purpose of treating hyperthyroidism. Some patients may have reactions such as fatigue, poor appetite, nausea, itchy skin and swelling of the thyroid gland within a few days after taking iodine. Most of them will gradually slow down after 1~2 weeks, no special medication is needed, and symptomatic treatment can be given if necessary. In addition, after iodine 131 surgery, we should regularly check the level of thyroid hormones and pay attention to the thyroid function, if it is still hyperthyroidism, then we can continue iodine 131 treatment, if it is hypothyroidism, then we should follow the doctor’s advice to take levothyroxine sodium tablets.