by EBSCO Medical Review Board

In addition to medications and surgery, radioactive iodine is a treatment option for certain types of hyperthyroidism.

Radioactive Iodine (Radioiodine)

Radioactive iodine is taken by mouth and absorbed by the thyroid gland. Once in the gland, it gives off radiation that damages the thyroid cells and slows thyroid hormone production. The radioactive iodine that is not taken up in the thyroid leaves the body within 2-3 days, primarily through the urine and other bodily fluids.

Calculating the correct dose of radioactive iodine is complicated. It must be done by a trained specialist. Alternatively, many doctors give a standard dose of radioactive iodine. The biological effects of radiation vary among different people, and the length of time it takes to cure hyperthyroidism varies greatly, as well.

This treatment is effective in up to 90% of people with Graves disease after 2 months. But, in some, it may take as long as 6 months. A few people may require a second or even third treatment. This happens more commonly in men, people under the age of 40 years, and those with large goiters . After treatment with radioactive iodine, the size of the thyroid gland may shrink.

The side effects of radioactive iodine treatment include:

  • Neck pain or soreness
  • Soreness of the salivary glands, which are located on the side of the mouth
  • Worsening of hyperthyroid symptoms for a few days
  • Worsening of the eye disease in Graves disease, especially in smokers—if you smoke , radioactive iodine may be avoided
  • Change in taste

After this treatment, there is a chance that you may develop hypothyroidism , a condition marked by too little thyroid hormone in the blood. This may develop as early as 2 months or as late as 20 years after treatment. The risk decreases after the first year, and each year after. Because of this, it’s important to see your doctor as recommended during the first year to have regular thyroid function testing. Treatment for hypothyroidism involves taking a replacement thyroid hormone.

  • If you are pregnant or nursing, radioactive treatment is not an option. It may harm the thyroid of the fetus or child.
  • If you are a woman of childbearing age, you should have a negative pregnancy test prior to the treatment. You should then use a contraceptive method for at least 6 months after the treatment.
  • If you are taking an antithyroid drug, it should be stopped before starting the radioiodine to get the best iodine uptake. Your doctor will tell you how far ahead of time to stop the medication.
  • If you are aged 65 years and older, or have a heart condition, you may need to take antithyroid drugs for several weeks prior to and after radioactive iodine treatment. This is done to avoid postirradiation thyroiditis, in which there may be too much thyroid hormone released after the procedure.
  • The amount of radiation you receive is not dangerous. To be on the safe side, doctors recommend that you do not spend long periods of time with pregnant women or very small children. Most doctors suggest sleeping alone for 2 days and avoiding kissing for 2-3 days. A small amount of radioactive iodine comes out in the saliva.
  • If you have an active eye disease related to hyperthyroidism, then you should avoid this treatment.


Bonnema SJ, Bartalena L, Toft AD, Hededus L. Controversies in radioiodine therapy: relation to ophthalmopathy, the possible radioprotective effect of antithyroid drugs, and use in large goiters. Eur J Endocrinol. 2002;147(1):1-11.

Hyperthyroidism and thyrotoxicosis. EBSCO DynaMed Plus website. Available at:  . Updated July 27, 2017. Accessed November 28, 2017.

Vaidya B, Pearce SH. Diagnosis and management of thyrotoxicosis. Brit Med J. 2014;349:g5128.

Revision Information

  • Reviewer: EBSCO Medical Review Board James Cornell, MD
  • Review Date: 11/2018
  • Update Date: 12/20/2014