Radioactive Iodine for Hyperthyroidism

The Most Common Hyperthyroid Treatment in the US

Written by Kresimira (Mira) Milas MD
Reviewed by Daesman N. Suri MD

Radioactive iodine treats hyperthyroidism by gradually shrinking your thyroid—ultimately destroying the gland. This therapy is much safer than it sounds; in fact, it is the most commonly used hyperthyroid treatment in the US. Unlike antithyroid medications, radioactive iodine is a permanent and more reliable cure for hyperthyroidism.

Radioactive Iodine Ablation
Radioactive iodine can destroy all or part of your thyroid. While there are instances when you don't need to destroy the entire gland to alleviate your hyperthyroid symptoms, the total destruction of the thyroid is most often necessary. Your doctor may refer to it as radioactive iodine ablation (ablation is a term that refers to destruction or erosion), and this article will focus on the total elimination of the thyroid.

Radioactive Iodine Testing
Depending on the dose, radioactive iodine can kill a portion, or all, of your thyroid. Your doctor will order a radioactive iodine uptake and scan to determine your dose, the cause of your hyperthyroidism, and information about your thyroid tissue.

In this test, you will ingest a very small dose of radioactive iodine. Your doctor will observe your thyroid's activity level by measuring the amount of iodine it absorbs. He or she will do this using a scan of your thyroid, which will show the healthy and diseased tissues.

In determining the best dose, the size of the thyroid gland (determined by a physical exam) and results of the uptake test are the two most important factors. The larger the gland, the larger the radioactive iodine dose. The higher the iodine uptake, the smaller the dose.

How Radioactive Iodine Works
Radioactive iodine is available in an oral pill, so you won't need to be hospitalized. After you take the pill, your doctor will recommend drinking lots of fluids to prompt the release of the radioactive iodine through your urine.

Radioactive iodine only affects your thyroid gland. Thyroid cells are the main cells in the body that can absorb iodine, so there is very little radiation exposure to the rest of your body's cells. When the thyroid cells absorb the radiation, they are damaged or destroyed.

Approximately 90% of patients need only one dose before they are cured of their hyperthyroidism. Though you may only need a single dose, it may take up to six months before the medication fully destroys all or part of the thyroid. Fortunately, most patients experience reduced symptoms about a month after treatment.

If your symptoms persist 6 months after treatment, you may need a second dose. In the rarest of cases, some patients will not benefit from a second dose and may instead require surgery.

Side Effects of Radioactive Iodine
The most common side effect of radioactive iodine may seem ironic, yet it makes perfect sense—hypothyroidism. The radioactive iodine often kills an excessive amount of thyroid cells, leaving the thyroid unable to produce enough hormones—the opposite problem you had before.

It might seem odd to replace one disorder with another, but hypothyroidism is much easier to treat on a long-term basis than hyperthyroidism. If you develop hypothyroidism, you will need to take life-long thyroid hormone replacement therapy , but it is a safe, reliable, and cost-effective treatment.

Other side effects of radioactive iodine include:

Note: Don't let your fears about radiation give you the wrong impression about this therapy. Radioactive iodine used in this manner will not cause thyroid cancer or impair fertility.

A Special Caution for Women
Pregnant women or women who want to become pregnant in the next 6 months should not use radioactive iodine, as the treatment can destroy the fetus's thyroid and impair its development. In fact, women should wait a year before conceiving if they have been treated with the therapy. Women who are breast-feeding should also not use radioactive iodine.

After Treatment
In the days following radioactive iodine therapy, you will need to take certain precautions to prevent radiation exposure to others. Keep in mind that the precautions listed below are general, and your doctor will be more specific about how many days and what kinds of precautions you need to follow tailored to your individual needs and medical circumstances.


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