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Potassium iodide (KI): what it does and how to store it

By the Plain Prepper editors. Updated 2026-10-18.

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Quick answer

Potassium iodide (KI) blocks the thyroid from taking up radioactive iodine. FDA says it is not a general radioprotective agent and should not be taken before an exposure; take it only when public health or emergency officials say to. FDA's adult dose is 130 mg, one 130 mg tablet or two 65 mg tablets, and one dose protects for about 24 hours. FDA lists iOSAT 130 mg and 65 mg and ThyroSafe 65 mg tablets among FDA-approved products sold without a prescription.

What potassium iodide does, and what it does not

A radiation emergency can release radioactive iodine, which the thyroid takes up. FDA explains that KI floods the thyroid with non-radioactive iodine and prevents the uptake of the radioactive molecules.

That is all it does. FDA says KI is not a general radioprotective agent, so it does not protect the rest of the body. Officials decide which protective actions are needed, and KI is only one of them; follow all of their instructions.

Take it only when officials tell you to

FDA says KI should not be taken as a preventive before radiation exposure, and that local public health or emergency management officials will decide whether protective actions, including KI, are needed. Keep a battery or hand-crank radio and your phone alerts on so you hear those instructions.

FDA says one dose protects the thyroid for about 24 hours, so it is taken daily until the risk is over, and only as directed. FDA warns that taking more than recommended, or more often, does not offer more protection and can cause severe illness or death.

FDA doses by age

FDA lists these single daily doses:

• Adults over 18: 130 mg (one 130 mg tablet or two 65 mg tablets). FDA says adults over 40 should take KI only if predicted thyroid exposure is very high.
• Pregnant or breastfeeding women: 130 mg.
• Adolescents 12 to 18 and children over 3 to 12: 65 mg (one 65 mg tablet or half a 130 mg tablet). FDA says adolescents over about 150 lb (70 kg) should take the adult dose.
• Children over 1 month to 3 years: 32 mg, as 0.5 mL of oral solution.
• Infants birth to 1 month: 16 mg, as 0.25 mL of oral solution.

For a household, that means at least one adult dose per adult per day and the 65 mg strength for school-age children. ThyroSafe says its 65 mg tablet removes the need to split a larger tablet in an emergency.

Who should not take it

FDA says to avoid KI with a known iodine sensitivity, dermatitis herpetiformis or hypocomplementemic vasculitis, and not to take it with a nodular thyroid and heart disease. FDA advises caution with multinodular goiter, Graves' disease or autoimmune thyroiditis, especially if dosing lasts more than a few days. If you are unsure, ask a health care professional now, before an emergency.

Which products FDA lists

FDA names these KI products as FDA-approved and available without a prescription (list as of March 2022): iOSAT 130 mg and 65 mg tablets from Anbex, ThyroSafe 65 mg tablets, and a potassium iodide oral solution, 65 mg/mL, from Mission Pharmacal. ThyroSafe's own site now also sells a 130 mg tablet; check the package label on whatever you buy.

Buy KI from a listing that clearly names one of these products and its strength. FDA's doses refer to potassium iodide products like these, at the strengths listed.

Storing KI in a kit

ThyroSafe sells both strengths in 20-tablet packs with individually foil-sealed tablets and says the 130 mg tablet is scored for splitting. Anbex sells iOSAT 130 mg and 65 mg tablets and a family pack of 8 with four of each strength.

Neither maker page gives a shelf-life length, so read the expiration date on the package and note it on your kit list. Keep the package and its insert together in your bug-out bag or home kit, out of reach of children.

What to look for when you buy

Questions people ask

When should you take potassium iodide?

Only when public health or emergency management officials say to. FDA says not to take KI as a preventive before radiation exposure.

What does potassium iodide protect against?

FDA says it blocks the thyroid from taking up radioactive iodine. It is not a general radioprotective agent and does not protect the rest of the body.

How much potassium iodide should an adult take?

FDA lists 130 mg per day for adults over 18: one 130 mg tablet or two 65 mg tablets. One dose protects for about 24 hours.

Can I take more KI for more protection?

No. FDA warns that taking more than recommended, or more often, does not offer more protection and can cause severe illness or death.

Who should not take potassium iodide?

FDA says people with known iodine sensitivity, dermatitis herpetiformis, hypocomplementemic vasculitis, or a nodular thyroid with heart disease should not take it. Ask a health care professional if unsure.

Sources

• Frequently Asked Questions on Potassium Iodide (KI) (fda.gov), U.S. Food and Drug Administration
• ThyroSafe Potassium Iodide Tablets (thyrosafe.com), ThyroSafe
• ThyroSafe 65 mg (thyrosafe.com), ThyroSafe
• ThyroSafe 130 mg (thyrosafe.com), ThyroSafe
• iOSAT Potassium Iodide (anbex.com), Anbex

Sources checked 2026-10-18.