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Radioiodine therapy

Radioactive iodine therapy; Hyperthyroidism - radioiodine; Thyroid cancer - radioiodine; Papillary carcinoma - radioiodine; Follicular carcinoma - radioiodine; I-131 therapy

Radioiodine therapy uses radioactive iodine to shrink or kill thyroid cells. It is used to treat certain diseases of the thyroid gland.


The thyroid gland is a butterfly-shaped gland located in the front of your lower neck. It produces hormones that help your body regulate your metabolism.

Your thyroid absorbs most of the iodine that enters your body. It needs iodine to function properly.

Radioiodine is used for different thyroid conditions. It is given by specialist doctors in nuclear medicine. Depending on the dose of the radioiodine, you may not have to stay in the hospital for this procedure, but go home the same day. For higher doses, you need to stay in a special room in the hospital and have your urine monitored for the radioactive iodine being excreted.

  • You will swallow radioiodine in the form of capsules (pills) or a liquid.
  • Your thyroid will absorb most of the radioactive iodine.
  • The nuclear medicine team may do scans during your treatment to check where the iodine has been absorbed.
  • The radiation will kill the thyroid gland and, if the treatment is for thyroid cancer, any thyroid cancer cells that might have traveled and settled in other organs.

Most other cells are not interested in taking up iodine, so the treatment is very safe. Very high doses can sometimes decrease the production of saliva (spit) or injure the colon or bone marrow.

Why the Procedure Is Performed

Radioiodine therapy is used to treat hyperthyroidism and thyroid cancer.

Hyperthyroidism occurs when your thyroid gland makes excess thyroid hormones. Radioiodine treats this condition by killing overactive thyroid cells or by shrinking an enlarged thyroid gland. This stops the thyroid gland from producing too much thyroid hormone.

The nuclear medicine team will try to calculate a dose that leaves you with normal thyroid function. But, this calculation is not always completely accurate. As a result, the treatment can lead to hypothyroidism, which needs to be treated with thyroid hormone supplementation.

Radioactive iodine treats cancer by killing any remaining thyroid cancer cells after surgery to remove the thyroid gland. You may receive this treatment 3 to 6 weeks after the surgery to remove your thyroid. It also can kill cancer cells that may have spread to other parts of the body.

Many thyroid experts believe this treatment has been overused in people with thyroid cancer with a very low risk for recurrence. Talk to your provider about the risks and benefits of this treatment for you.


Risks of radioiodine therapy include:

  • Low sperm count and infertility in men for up to 2 years after treatment (rare)
  • Irregular periods in women for up to one year (rare)
  • Very low or absent thyroid hormone levels that require medicine for hormone replacement (common)

Short-lasting side effects include:

  • Neck tenderness and swelling
  • Swelling of the salivary glands (glands at the bottom and back of the mouth where saliva is produced)
  • Dry mouth
  • Gastritis
  • Taste changes
  • Dry eyes

Women should not be pregnant or breastfeeding at the time of treatment, and they should not become pregnant for 6 to 12 months following treatment. Men should avoid conception for at least 6 months following treatment.

For people with Graves disease who have thyroid-related eye problems, the radioiodine treatment can make eye problems worse. This risk is higher in people with more severe eye disease before treatment and in smokers.

Before the Procedure

You may have tests to check your thyroid hormone levels before the therapy.

You may be asked to stop taking any thyroid hormone medicine before the procedure.

You will be asked to stop any thyroid-suppressing medicines (propylthiouracil, methimazole) at least one week before the procedure (very important or the treatment will not work).

You may be placed on a low-iodine diet for 2 to 3 weeks before the procedure. You will need to avoid:

  • Foods that contain iodized salt
  • Dairy products, eggs
  • Seafood and seaweed
  • Soybeans or soy-containing products
  • Foods colored with red dye

You may receive injections of thyroid-stimulating hormone to increase the uptake of iodine by thyroid cells.

Just before the procedure when given for thyroid cancer:

  • You may have a body scan to check for any remaining cancer cells that need to be destroyed. Your provider will give you a small dose of radioiodine to swallow.
  • You may receive medicine to prevent nausea and vomiting during the procedure.

After the Procedure

Chewing gum or sucking on hard candy may help with dry mouth. Your health care provider may suggest not wearing contact lenses for days or weeks afterward.

You may have a body scan to check for any remaining thyroid cancer cells after the radioiodine dose is given.

Your body will pass the radioactive iodine in your urine and saliva.

To prevent exposure to others after therapy, your provider will ask you to avoid certain activities. Ask your provider how long you need to avoid these activities -- in some cases, it will depend on the dose given.

For about 3 days after treatment, you should:

  • Limit your time in public places
  • Not travel by airplane or use public transportation (you may set off the radiation detection machines in airports or at border crossings for several days after treatment)
  • Drink plenty of fluids
  • Not prepare food for others
  • Not share utensils with others
  • Sit down when urinating and flush the toilet 2 to 3 times after use

For about 5 or more days after treatment, you should:

  • Stay at least 6 feet away from small children and pregnant women
  • Not return to work
  • Sleep in a separate bed from your partner (for up to 11 days)

You should also sleep in a separate bed from a pregnant partner and from children or infants for 6 to 23 days, depending upon the dose of radioiodine given.

You'll likely need to have a blood test every 6 to 12 months to check thyroid hormone levels. You also may need other follow-up tests.

Most people will need to take thyroid hormone supplement pills for the rest of their life. This replaces the hormone the thyroid would normally make.

Outlook (Prognosis)

The side-effects are for short term and go away as time passes. High doses have a low risk for long-term complications including damage to salivary glands and risk for malignancy.


American Cancer Society website. Radioactive iodine (radioiodine) therapy for thyroid cancer. Updated April 15, 2016. Accessed January 23, 2019.

Mettler FA, Guiberteau MJ. Thyroid, parathyroid, and salivary glands. In: Mettler FA, Guiberteau MJ, eds. Essentials of Nuclear Medicine and Molecular Imaging. 7th ed. Philadelphia, PA: Elsevier; 2019:chap 4.

Ross DS, Burch HB, Cooper DS, et al. 2016 American Thyroid Association guidelines for diagnosis and management of hyperthyroidism and other causes of thyrotoxicosis. Thyroid. 2016;26(10):1343-1421. PMID: 27521067


        Review Date: 10/11/2018

        Reviewed By: Brent Wisse, MD, board certified in Metabolism/Endocrinology, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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