Potassium Iodide (KI)

Taking potassium iodide (also known as KI) after an incident involving radioactive materials may protect a person’s thyroid gland from ionizing radiation. Taking KI will not protect you from other radioactive substances.

Vermont’s KI Distribution Program

The State of Vermont makes potassium iodide tablets available free of charge to people who work or reside in the Vermont towns within the Emergency Planning Zone (EPZ) for Vermont Yankee Nuclear Power Plant - Brattleboro, Dummerston, Guilford, Halifax, Marlboro and Vernon.

Parents/guardians are eligible to receive a free dose for each child in their family. Participation in this program is been voluntary. Public schools, nursing homes, hospitals, and some day care centers and private schools in these towns also have KI distribution plans in place.

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How will I know when to take KI — and when to stop?

If there is a serious radiation emergency, state health officials will tell you when to take KI. Tune to your Emergency Alert System radio station immediately for directions on evacuating, sheltering, or taking KI. If you are hearing impaired, please register with your town’s emergency management office so that you will be alerted by TDD.

For best protection, one dose of potassium iodide should be taken before or at the time of exposure, although it may still lower risk of thyroid cancer even if taken 3 to 4 hours after exposure.

Because the radioactive iodine decays quickly, a single dose of KI may be all that is required. When the danger has passed, you will be notified to stop taking potassium iodide via the same Emergency Alert System, or you will receive instruction at the reception center.


Do not delay evacuation or ignore any other emergency directive to locate your supply of potassium iodide. If you are evacuated, you will be directed to a reception center.

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If told to take KI, how much should I take?

The potassium iodide tablets that were distributed are small, white pills, 130 milligrams (mg) in size. They come wrapped in foil and labeled “IOSAT” and “Dist. By ANBEX.”

One full 130-mg. tablet is the normal dose for adults. Women who are breastfeeding should take the adult dose, and their infants should take the recommended infant dose. Children approaching adult size (150 pounds or more) should take the adult dose, no matter how old they are.

Recommended Dose of Potassium Iodide
Adults including pregnant or lactating women 130 mg 1 tablet
Adolescents over 12 through 18 years 65 mg 1/2 tablet
Children over 3 through 12 years 65 mg 1/2 tablet
Infants over 1 month old 32 mg 1/4 tablet
Newborns through 1 month old 16 mg 1/8 tablet

One dose of KI at the proper dosage is usually all that is needed. Taking more than one dose at a time will not help, and could harm you. Pregnant or breastfeeding women should NOT have a repeat dose.

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How can I tell if my KI dose has expired?

The expiration date is clearly marked on the packaging of the tablet and liquid fors of KI. Dispose of expired KI properly.

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How do I dispose of expired KI?

If you have expired KI, you can dispose of it in the same way as with prescription medicines: Take expired KI out of the packaging and mix it with an undesirable substance (for example, used kitty litter, coffee grounds, bacon fat), and place the mixture into a sealable plastic bag or container, and place it into the trash.

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Are there side effects to taking KI?

Short-term use of KI at the proper dosage is safe for most people. Side effects are generally mild (but note contraindications above). Possible side effects include gastrointestinal distress, and rash. Allergic reactions may be seen in adults with known iodine sensitivity.

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What is Potassium Iodide (KI)?

Potassium iodide, also known as KI, is a form of iodine. Classified as a drug approved for over-the-counter sale, KI has been determined by the U.S. Food and Drug Administration (FDA) to be a safe and effective method to block exposure to one product of a nuclear release — radioactive iodine. Radioactive iodine, either inhaled or ingested through contaminated food or milk, can increase the risk of developing thyroid cancer.

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How does KI work to protect against thyroid cancer?

The thyroid is a small gland located in a person’s neck on either side of the breathing tube (trachea). Certain forms of iodine help your thyroid function properly. Most people get the iodine they need from foods like fish and iodized salt. The thyroid is designed to absorb and store iodine, but it can hold only so much, and will just as readily absorb non-radioactive potassium iodide as radioactive iodine. Because of this, one dose of potassium iodide, which is not harmful to the thyroid, works by filling the gland so it cannot take up any radioactive iodine.

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Why is KI important in the event of a nuclear incident?

Because the thyroid will quickly absorb any iodine that is in the body, people may need to take KI tablets soon after an incident that involves radioactive iodine. The KI will fill up the thyroid gland with iodine and help prevent it from absorbing radioactive iodine. However, KI does not prevent the effects of other radioactive elements. Using KI will only protect the thyroid gland from radioactive iodine. It will not protect other parts of the body from radioactive iodine, and it will not protect a person from other radioactive materials that may be released.

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