Radioactive Iodine

How does radioactive iodine work?

The thyroid gland absorbs iodine from the blood. When radioactive iodine enters your thyroid, it slowly shrinks the gland over a period of weeks or months.

The treatment is safe, simple, convenient, and inexpensive. It is usually given only once, rarely causes any pain or swelling, and does not increase the risk of cancer. However, it must be avoided during pregnancy or nursing, and patients should not become pregnant for at least six months after treatment.

When is radioactive iodine used?

Radioactive iodine is the most common treatment for hyperthyroidism. It does not require hospitalization. About 90% of patients need only one treatment. They usually start getting better in three to six weeks, and most are cured within six months.

This treatment may also be used after surgery for certain thyroid cancers. Radioactive iodine dissolves any cancerous tissue that could not be removed by surgery. The dose of radioactive iodine is larger in this case, and patients usually stay in the hospital for a day or two.

What can be expected with radioactive iodine treatment for hyperthyroidism?

  • It is usually given in liquid form or as a capsule. The dose can range from 4 to 29 millicuries.
  • It is tasteless.
  • There are almost never any side effects. In some rare cases, there can be an inflammation of the thyroid gland causing a sore throat and discomfort.
  • Radioactive iodine not taken up by the thyroid gland is excreted in urine and saliva. There is no evidence that the small amount of I131 excreted in the urine and saliva is harmful. Nonetheless, prudent nuclear medicine experts have recommended a wide variety of precautions. While these recommendations are sometimes confusing and inconsistent, it may be appropriate to take a few simple measures to avoid unnecessary exposure of infants and children to I131. Treated patients should rinse out their glasses or cups and eating utensils immediately after drinking and eating. The toilet should be flushed immediately after use, and the rim of the bowl should be wiped dry, if necessary.
  • It is advisable to drink two to three extra glasses of water a day during the four- to seven- day period following radioactive treatment so that radioactive material will not collect in the bladder for a long period of time.
  • Because radioactive iodine passes into breast milk, breast feeding mothers are asked to wean their babies before treatment.
  • It typically takes six weeks before thyroid hormone production is noticeably reduced. The average length of time for the thyroid hormone levels to become normal is about three to four months. If thyroid levels are not considerably reduced six months after treatment, the doctor might suggest repeating the treatment. Ninety percent of the time only one treatment is required; however, it might take as many as three attempts. The patient could be advised to take beta-blocking drugs and other medications the doctor believes are necessary until normal thyroid hormone production is restored.
  • Many patients treated with radioactive iodine become hypothyroid. This may happen within weeks, months, or years of treatment. Therefore, patients should be aware of the signs and symptoms of hypothyroidism, and their physicians should monitor their thyroid hormone levels regularly. When the patient becomes hypothyroid, thyroid hormone replacement begins and continues for life-one pill a day.