What is radioactive iodine (RAI) therapy?

Radioactive iodine (RAI) is treatment for overactive thyroid (hyperthyroidism) and certain types of thyroid cancer. The term “radioactive” may sound frightening, but it is a safe, generally well-tolerated, and reliable treatment that targets thyroid cells so there is little exposure to the rest of your body’s cells.

How does radioactive iodine treat hyperthyroidism?

Your thyroid, a butterfly-shaped gland located in the lower front of your neck, produces hormones that regulate your body’s metabolism and other functions. Hyperthyroidism speeds up the body’s processes causing nervousness and anxiety, rapid heartbeat, missed or light menstrual periods, sleep problems, hand tremors, and other problems.

The thyroid gland needs iodine to make these hormones. The thyroid is the only part of the body that can concentrate iodine. RAI treats hyperthyroidism by damaging or destroying thyroid cells through radiation.

RAI is taken in an oral capsule form. You don’t need to be hospitalized unless the dose is very high, which is rarely needed. You will be prompted to drink lots of water after taking the pill to flush the remaining radioactive iodine out of your system.

Most patients need only one dose before their hyperthyroidism is resolved, which usually happens around 6 months. If your symptoms are still there after 6 months, you may have to receive a second dose.

How does radioactive iodine treat thyroid cancer?

The most common types of thyroid cancer can usually be treated with large doses of radioactive iodine. (The dosages of RAI are much higher than with hyperthyroidism treatment.) The therapy is usually given after removal of the thyroid gland to destroy any remaining thyroid tissue.

Test amounts of radioactive iodine can also be used to track patients who have some remaining thyroid tissue and cancer that could have spread to other parts of the body. These tests show if iodine concentrates in areas that contain thyroid cancer, and whether large amounts of RAI are needed to destroy the tumor implants.