by Marc Coel, M.D.

Radioactive iodine (RAI) is often chosen for treatment of hyperthyroidism (overactive thyroid) because of its simplicity: it is given in a single dose. Another plus for RAI is its lack of side effects.

How Radioactive Iodine Treatment Works

RAI treatment is based on the fact that the thyroid actively accumulates iodine, which it uses to produce thyroid hormones required for normal body function. This RAI is like the iodine found in foods such as fish, seaweed, and iodized salt, except that it releases an electron, or beta particle, which creates its therapeutic action.

For use in treatment, the RAI is given dissolved in water or as a capsule. It is absorbed quickly by the stomach and intestines, then carried in the bloodstream to the thyroid, where it is taken up by the gland. While in the thyroid gland, the RAIdisrupts the function of some of the thyroid cells – the more radioactive iodine given, the more cells cease to function. As the cells stop functioning, excessive amounts of thyroid hormones are no longer produced, and symptoms of hyperthyroidism begin to disappear.

Side Effects

Radioactive iodine treatment has few side effects, and these occur infrequently.

* A sore throat may occur a few days after the treatment, which can be treated with acetaminophen.
* Rarely, the salivary glands may swell, which is caused by the iodine and not the radioactivity. Some physicians believe that sucking hard candies for a few days can prevent this.
* Mild nausea may develop for a few hours after the iodine is taken, so it is best not to eat two hours before and two hours after the iodine administration.


Some precautions are necessary because of the small amount of radiation that emanates from the neck where the RAI is stored for a few days after treatment. While this radiation is beneficial for the person being treated, precautions are needed to reduce the radiation families and friends are exposed to.

1. Avoid prolonged contact with others, especially children and pregnant women.

In general, a distance of one arm’s length should be maintained between the person treated and others who spend more than two hours next to the patient in any 24 hour period. This applies especially to children and pregnant women. While brief contact with a person after treatment is acceptable, sleeping together, watching television, going to movies, long care or plane trips should be avoided for approximately 11 days after the treatment.

Sharing food and utensils, including glasses, bottles, cans of soda, water, beer, etc., should also be avoided. For example, when the treated person is eating an ice cream cone, it should not be licked by anyone else. Dishes and eating utensils should be rinsed before being put with those of the rest of the family. Paper plates and plastic utensils should only be used if they are immediately disposed of outside the home. Cooking is fine, as long as the utensil used to taste the food while cooking is not re-used before rinsing.

2. Drink lots of liquids, void often, and flush twice.

The treated person should drinks lots of liquids, especially water, to help remove the RAI from the system, flush the toilet twice after using it, and be sure to thoroughly clean up any spilled urine. Laundry need not be washed separately unless the treated person has sweated heavily, such as after exercise.

3. No pregnancy or breast-feeding.

It is extremely important that women who are breast-feeding stop before the RAI is given, since iodine is concentrated and excreted in breast milk.

Pregnant women should not be treated with RAI, and pregnancy should be avoided for six months following treatment.

After the Treatment

Symptoms of the disease will improve slowly, beginning about two weeks after the treatment. Muscle strength improves, tremors and irritability lessen, heat intolerance improves, and sleep is more sound.

To prevent recurrence of the disease, enough radioiodine is commonly given to cause an underactive thyroid within six to 12 weeks following treatment. Once the thyroid becomes underactive, a single daily pill of thyroid hormone, T4, must be taken for life. Although most patients are completely cured, a few people will need a second treatment. Even if thyroid function returns to normal after radioactive iodine, there is a high likelihood that the thyroid will eventually become underactive.

Therefore, people treated with radioactive iodine must remain under the care of their doctor indefinitely.


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