I-131 is an isotope of iodine used in the treatment of an overactive thyroid (hyperthyroidism) or in killing residual or metastatic tissue in patients with Thyroid Cancer.

The isotope I-131 is used to destroy or disable functioning thyroid tissue so that it decreases or eliminates the production of thyroid hormone.

It is a painless remedy and involves the oral administration of a small capsule that has no significant taste or smell of any sort and can be given on an outpatient basis under some guidelines of release. However, it has to be administered by a licensed Nuclear Medicine Physician.