Radioactive iodine for hyperthyroidism

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Radioactive iodine for hyperthyroidism

Treatment Overview

Radioactive iodine is a medicine that you take one time. After you swallow it, it is taken up by your thyroid gland. Depending on the dosage used, the radioactivity in the iodine destroys most or all of the tissue in your thyroid gland, but it does not harm any other parts of your body.

Radioactive iodine treatment has been safely used on millions of people for more than 60 years.

What To Expect After Treatment

Within a few days after treatment, the radioactive iodine will leave your body in your urine. Drinking plenty of fluids during this time will help your body get rid of the radioactivity. To avoid exposing other people to radioactivity, it is important to take the following precautions for the first 5 days after your treatment:

  • Avoid spending a lot of time around others, especially children and pregnant women.
  • Do not sit next to someone in a motor vehicle for more than 1 hour.
  • Avoid close contact, kissing, or sexual intercourse.
  • Sleep alone in a separate room.
  • Use separate towels, face cloths, and sheets. Wash these and your personal clothing separately for 1 week.

To further reduce the chance of exposing other people to radioactivity:

  • Wash your hands with soap and lots of water each time you use the toilet.
  • Keep the toilet very clean. Men should urinate sitting down to avoid splashing. Also, flush the toilet two or three times after each use.
  • Rinse the bathroom sink and tub thoroughly after you use them.
  • Use separate (or disposable) eating utensils for the first few days. And wash them separately.

After you take your treatment, you may have follow-up examinations every 4 to 6 weeks until your thyroid hormone levels return to normal.

Why It Is Done

Radioactive iodine has the best chance of permanently curing hyperthyroidism. Doctors often use it if your hyperthyroidism comes back after you have been treated with antithyroid medicine. It can also be used if your hyperthyroidism comes back after you have surgery to remove part of your thyroid gland.

How Well It Works

For most people, one dose of radioactive iodine treatment will cure hyperthyroidism. Usually, thyroid hormone levels return to normal in 8 to 12 weeks. In rare cases, the person needs a second or third dose of radioactive iodine.


For some people, radioactive iodine treatment causes the thyroid gland to become swollen and inflamed (radiation thyroiditis). If this happens, you may feel pain in your neck. Or your hyperthyroidism may temporarily get worse. If you get radiation thyroiditis, it usually does not last more than a few days. And you can take medicines that will help you feel better.

Radioactive iodine treatment may cause hypothyroidism, which means your body makes too little thyroid hormone. Most people will have hypothyroidism in 1 to 10 years after treatment.1 If you have hypothyroidism, you will need to take thyroid hormone medicine for the rest of your life. For more information, see the topic Hypothyroidism.

If you have Graves' ophthalmopathy, it may get worse temporarily after radioactive iodine therapy.

What To Think About

Radioactive iodine is often recommended if you have Graves' disease and are older than 50, or if you have thyroid nodules (toxic multinodular goiter) that are releasing too much thyroid hormone. Radioactive iodine is not used if:

  • You are pregnant or you want to become pregnant within 6 months of treatment.
  • You are breast-feeding.
  • You have thyroiditis or another kind of hyperthyroidism that is often temporary.

You may take antithyroid medicine for several weeks or months before treatment with radioactive iodine. The antithyroid medicine will lower thyroid hormone levels in your body and will also lower your chances of having a more serious problem called thyroid storm. You may also take additional medicines that can make you feel better and help your thyroid return to normal before you are given radioactive iodine.

Radioactive iodine has been used to treat hyperthyroidism for more than 60 years. There is no evidence that radioactive iodine causes cancer, infertility, or birth defects.

If you have had radioactive iodine treatment and you want to travel within a few days after treatment, prepare for any problems you may have at airport security. People who have had radioactive iodine treatment can set off the radiation detection machines in airports.

If you plan to travel within 5 to 7 days of your radioactive treatment:

  • Check with local authorities about special procedures or considerations.
  • Ask your doctor to write a letter describing the radiation isotope used, the date and time of treatment, the dose, and its biological half-life (how long it takes for half of the radioactive iodine to be eliminated from the body). The letter should include your doctor's 24-hour telephone numbers so that authorities can call your doctor if they need to verify the information in the letter.
  • Keep in mind that you will have to wait for permission to travel.

Complete the special treatment information form (PDF) (What is a PDF document?) to help you understand this treatment.



  1. Jameson JL, Weetman AP (2008). Hypothyroidism section of Disorders of the thyroid gland. In AS Fauci et al., eds., Harrison's Principles of Internal Medicine, 17th ed., vol. 2, pp. 2224–2237. New York: McGraw-Hill.


By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer Matthew I. Kim, MD - Endocrinology
Specialist Medical Reviewer Andrew Swan, MD, CCFP, FCFP - Family Medicine
Last Revised February 5, 2010

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