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

Radioactive Iodine (Radioiodine)

Radioactive iodine is used to treat approximately 90% of the hyperthyroid patients in the United States. Radioactive iodine is taken orally and absorbed by the thyroid gland. Once in the gland, it gives off radiation that damages the thyroid cells and slows the thyroid hormone production. The radioactive iodine that is not taken up in the thyroid leaves the body within two or three days, primarily through the urine.

Calculating the correct dose of radioactive iodine is complicated and thus done by a trained specialist. 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 usually effective in up to 90% of patients with Grave’s disease after two months, but in some patients it may take as long as six months. A few patients may require a second or even third treatment. This happens more commonly in men and patients under the age of 40 years. After treatment with radioactive iodine, the size of the thyroid gland will be reduced by 40% in patients with toxic multinodular goiter.

The side effects of radioactive iodine treatment include the following:

  • Neck pain
  • Worsening of hyperthyroid symptoms for a few days
  • Worsening of the eye disease in Grave’s disease after radioactive iodine treatment, especially in smokers

Most people who have hyperthyroidism become hypothyroid in five to ten years. This may happen if the hyperthyroidism has not been treated or if the treatment was antithyroid medication or surgery. Hypothyroidism may develop as early as two months or as late as 20 years after treatment for hyperthyroidism. For this reason, many doctors favor destroying the thyroid altogether. The risk of hypothyroidism after radioactive iodine treatment is 10%-20% in the first year and 5% per year for every year after. Because of this, it’s important to see your doctor frequently during the first year and have annual thyroid function testing thereafter.

Special Considerations

  • Radioactive iodine should not be given to pregnant women or nursing mothers as it may harm the thyroid of the fetus or child.
  • If you are taking an antithyroid drug, it should be stopped 3 to 5 days before starting the radioiodine to get the best iodine uptake.
  • There are almost no adverse side effects from radioactive iodine treatment. Rarely, the thyroid gland feels slightly tender for several days.
  • The amount of radiation you receive is not dangerous. To be on the safe side, though, physicians recommend you don’t spend long periods of time with pregnant women or very small children. Most physicians suggest sleeping alone for 2 days and avoiding kissing for 2 to 3 days as a small amount of radioactive iodine comes out in the saliva.
  • Patients over 65 years or those with a heart condition need to take antithyroid drugs for several weeks prior to and after radioactive iodine treatment in order to avoid the condition known as postirradiation thyroiditis .
  • Women in the child-bearing age should have a negative pregnancy test prior to radioactive iodine treatment, and they should use a contraceptive method for at least 6 months afterwards.
  • Hyperthyroid patients with active eye disease, also know as exophthalmos (Grave’s disease) should avoid radioactive iodine treatment.