Medical Definition of Radioactive iodine

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Reviewed on 12/11/2018

Radioactive iodine: An isotope of the chemical element iodine that is radioactive. Radioactive iodine is used in diagnostic tests as well as in radiotherapy of an hyperactive thyroid gland (hyperthyroidism), most often due to Graves' disease.

For hyperthyroidism, Radioactive iodine is administered in capsule form on a one- time basis. It directly radiates thyroid tissues, thereby destroying them. It takes 8-12 weeks for the thyroid to become euthyroid (normal) after treatment.

The majority of patients undergoing this treatment with radioactive iodine eventually become hypothyroid, which is easily treated using thyroid hormones (levothyroxine).

Radioactive iodine should not be used during pregnancy or breast feeding.

Radioactive iodine is the preferred initial therapy for the hyperthyroidism of Graves disease in North America while antithyroid drugs are used as the first line of treatment in most of the rest of the world. Radioactive iodine is also known as radioiodine.

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Reviewed on 12/11/2018