Iodine-131, a radioisotope of elemental iodine, is radioactive and is readily taken up by the thyroid gland, so there is some radiation associated with thyroid uptake tests. However, the amount of radiation produced by this type of test is small and the residual iodine-131 can usually be metabolized normally in the body, making it a relatively safe test. Some patients may experience systemic symptoms such as lethargy and fatigue. There are also gastrointestinal reactions such as nausea, vomiting, abdominal pain and diarrhea, as well as local reactions to uptake such as thyroid edema, sore throat, and even neurological symptoms such as dizziness and headache. Therefore, patients are often advised to drink more water after the thyroid uptake 131 iodine test to promote excretion so that the residual iodine-131 in the body can be metabolized out of the body more quickly and reduce the side effects for the body. Usually, it takes about 4 weeks for the iodine-131 intake to be completely metabolized in patients who have undergone a thyroid iodine uptake test. Therefore, it is important to avoid contact with infants during this time, as the residual iodine-131 can have serious effects on infants, as their body functions are not yet fully developed. It is also not recommended for women who are pregnant or breastfeeding to undergo a thyroid iodine uptake test.