In addition to medications and surgery, radioactive iodine is a treatment option for certain types of hyperthyroidism.
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:
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.
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: http://www.dynamed.com/topics/dmp~AN~T116479/Hyperthyroidism-and-thyrotoxicosis . Updated July 27, 2017. Accessed November 28, 2017.
Vaidya B, Pearce SH. Diagnosis and management of thyrotoxicosis. Brit Med J. 2014;349:g5128.
Last reviewed November 2018 by
EBSCO Medical Review Board
James Cornell, MD
Last Updated: 12/20/2014