Fact Sheet: Guidelines for Patients Receiving Radioiodine I-131 Treatment


What is radioiodine?

Radioiodine (sodium I-131) is a form of radiation therapy that has been used for many years to treat thyroid conditions. It is safe and effective but requires you to observe certain precautions to decrease the small amount of radiation that other people may receive from your body and bodily fluids.

How long does the radioiodine stay in your body?

Radioiodine stays in your body for only a short time. Most of the radioiodine that does not go to thyroid tissue will be eliminated from your body during the first few days after treatment. Radioiodine leaves your body primarily through your urine, but very small amounts can be found in your saliva, sweat and bowel movements.

Ask your doctor for more information. You also may get more information from the Society of Nuclear Medicine and Molecular Imaging at www.snmmi.org.

How can you reduce radiation exposure to others?

Radiation exposure to other people can be reduced by keeping a reasonable distance between yourself and others and keeping the time you are close to others to a minimum. Your doctor should review the following instructions with you and answer all of your questions. It is important to let your doctor know if you will not be able to follow all of these instructions.

These instructions apply if you are returning to your own home after treatment using private transportation. You should ask your doctor for additional instructions if you are planning to use public transportation or stay in a hotel or other non-private lodging.

First 8 hours:

  • Drink one glass of water each hour and use the bathroom as soon as possible when you need to empty your bladder. Men should sit on the toilet while urinating to decrease splashing. Use a tissue to wipe up any urine on the toilet bowl and flush twice. Wash your hands and rinse the sink.
  • Maintain a distance of at least 3 feet from all people. If possible, you should drive home alone. If it is not possible to drive alone, you should choose the seat that keeps as much distance as possible between you and the other passengers. You should not use public transportation.

First two days:

  • Do not share cups, glasses, plates or eating utensils. Wash items promptly after using. Other people may use items after they are washed.
  • Do not share towels or washcloths.
  • Flush the toilet twice and rinse the sink and tub after use.
  • Wash your towels, bed linens, underwear, and any clothing stained with urine or sweat.

First week:

  • Arrangements should be made for others to provide childcare for infants and very young children.
  • Sleep alone for 7 days unless otherwise instructed by your doctor.
  • Avoid kissing and physical contact with others, and maintain a distance of at least 3 feet from women who are pregnant and children under 18 years old.
  • Avoid activities where you may be close to others for more than 5 minutes, for example, movie theaters, sporting events and public transportation.

Additional instructions for women who are breastfeeding

You must stop breastfeeding before you can be treated with radioiodine. If possible, you should stop breastfeeding for 6 weeks prior to treatment. You should not resume breastfeeding after treatment for your current child, but you may safely breastfeed babies you may have in the future. Failure to follow this guidance may result in permanent damage to the thyroid gland of the nursing infant or child.


Radioiodine treatment should not be given during pregnancy. Tell your doctor if you are pregnant or could be pregnant. If you are planning to become pregnant, you should wait at least 6 months after treatment to ensure your thyroid hormone level is normal and that you do not need additional treatment. Consult your doctor.

Other things you should know during the first week after treatment:

Small amounts of radiation from your body may trigger radiation monitors at airports, border crossings, government buildings, hospitals, and waste disposal sites for up to 3 months after treatment. Ask your doctor for advice if you will be in these areas. Your doctor can provide you with a letter describing your medical treatment if you cannot avoid these areas.

Discarded items that are heavily stained with urine, saliva, nasal secretions, sweat or blood may trigger alarms at waste disposal sites. Ask your doctor for advice on how to safely dispose of these items.

This information may be used to meet the requirements of the U.S. Nuclear Regulatory Commission for giving written instructions to patients following treatment with radioiodine.More specific instructions may be required in certain circumstances.