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    Radioactive Iodine

    Radioactive iodine, given in a capsule or liquid form, is absorbed and concentrated by the thyroid gland. The treatment destroys thyroid tissue but does not harm other tissue in the body.

    See a picture of the thyroid gland camera.gif.

    While radiation can cause thyroid cancer, treatment of hyperthyroidism with radioactive iodine does not increase your chances of getting thyroid cancer.

    What To Expect After Treatment

    Within days, the radioactive iodine passes out of your body in your urine and saliva. How long it takes will depend on the dose you received and your age. Young people get rid of radioactive iodine faster than older adults.

    Most people don't feel different after treatment. But a few people may feel a little nauseated.

    Your doctor will give you written instructions. To avoid exposing other people to radioactivity, it is important to follow your doctor's instructions carefully. He or she will instruct you on how far to stay away from people, how long you need to sleep alone, and other ways to stay safe. You will be directed to avoid close contact, kissing, sex, and sharing cups, dishes, or utensils.

    Some general recommendations include:1

    • Flush the toilet twice each time you use it.
    • Wash your hands well with soap and lots of water each time you use the toilet.
    • Use separate towels, washcloths, and sheets. Wash these and your personal clothing by themselves and not with other people's laundry.
    • You may want to use a special plastic trash bag for all your trash, such as bandages, paper or plastic dishes, menstrual pads, tissues, or paper towels. Talk to your treatment facility to see if they will handle the disposal. Or after 80 days, this bag can be thrown out with your other trash.
    • Don't cook for other people. If cooking is necessary, use plastic gloves and throw them away in the special plastic trash bag.
    • Wash your dishes in a dishwasher or by hand. If you use disposable dishes, they must be thrown away in the special plastic trash bag.

    Why It Is Done

    Radioactive iodine may be used to treat hyperthyroidism in people who have noncancerous (benign)thyroid nodules that make too much thyroid hormone.

    Radioactive iodine is also used if you have your thyroid removed (thyroidectomy) because of thyroid cancer. Radioactive iodine therapy destroys any remaining thyroid tissue or cancer cells that were not removed during surgery.

    How Well It Works

    In almost all cases, your thyroid hormone levels will return to normal or below normal after radioactive iodine treatment. This may take 8 to 12 weeks or longer. If your thyroid hormone level does not go down after 6 months, you may need another dose of radioactive iodine.

    If you have thyroid cancer and you are treated with radioactive iodine, it may take from several weeks to many months for your body to get rid of any remaining cancer cells.

    Your thyroid nodule is unlikely to grow after being treated with radioactive iodine.


    The risks from radioactive iodine treatment include:

    What To Think About

    If you are pregnant, you should not receive radioactive iodine treatment. This kind of treatment can damage your fetus's thyroid gland or expose your fetus to radioactivity.

    You should not breast-feed your baby after you have been treated with radioactive iodine. Ask your doctor when it is safe to breast-feed.

    Different people with thyroid cancer will receive different doses of radioactive iodine. If you are young and you do not have a great risk of your cancer coming back, you will probably need less radioactive iodine than an older person. Sometimes this means that a younger person who receives radioactive iodine treatment will not have to stay overnight in a hospital.

    Traveling after treatment

    If you have had radioactive iodine treatment and you want to travel 3 to 4 days after treatment, it is important to 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 for a week to 10 days.

    • If you plan to travel by airplane within 3 or 4 days after your treatment, check with local authorities about any steps or permission you may need to travel.
    • If you plan to travel on the interstate, you may set off radiation detectors. Most police and transportation workers are aware of medical radiation, but it may be a good idea to carry some paperwork from your doctor.

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


    1. Sisson JC, et al. (2011). Radiation safety in the treatment of patients with thyroid diseases by radioiodine 131I: Practice recommendations of the American Thyroid Association. From the American Thyroid Association Taskforce on Radioiodine Safety. Thyroid, 21(4): 335-346.

    ByHealthwise Staff
    Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
    Specialist Medical ReviewerMatthew I. Kim, MD - Endocrinology

    Current as ofNovember 14, 2014

    WebMD Medical Reference from Healthwise

    Last Updated: November 14, 2014
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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