Potassium Iodide (KI): What FDA and CDC Actually Say

Potassium iodide (KI) is a narrow medicine that people often expect too much from. This page summarizes what FDA and CDC publish. It does not calculate a dose, and it is not medical advice.

Do not take KI unless public health or emergency officials or a healthcare provider tell you to. That is CDC's instruction.

What KI does and does not do

FDA: KI works only to prevent the uptake of radioactive iodine into the thyroid gland. It is not a general radioprotective agent.
CDC: KI does not protect against other radioactive materials or against external radiation, and it does not treat damage already done.
KI will not help in a nuclear bomb emergency. That is CDC's own heading. CDC says radiation from fallout is the biggest threat after a detonation, and KI gives no protection against it.

Where KI does come up

The main use is a release of radioactive iodine, such as a nuclear power plant accident. The NRC lists the use of potassium iodide pills "where appropriate" among the protective actions planned for the area of about 10 miles around a plant, alongside sheltering and evacuation. Officials decide whether it applies in a real event. See US nuclear plants by state.

When to take it

Only when told to. The agencies word the timing differently:

FDA: KI should not be taken as a preventative before radiation exposure, and it works best if used within 3-4 hours of exposure.
CDC: KI must be taken within 24 hours before or 4 hours after exposure to be most effective.

One dose protects for about 24 hours, and officials will say if another is needed. CDC warns that leaving your shelter or home to seek KI could expose you to dangerous levels of radiation.

FDA dosing table

This is FDA's published table, reproduced as a reference for use when officials instruct it. "Predicted thyroid exposure" is something officials estimate. You cannot work it out yourself.

Group	Predicted thyroid exposure (cGy)	KI dose	130 mg tablets	65 mg tablets	65 mg/mL solution
Adults over 40	over 500	130 mg	1	2	2 mL
Adults over 18 through 40	over 10	130 mg	1	2	2 mL
Pregnant or lactating women	over 5	130 mg	1	2	2 mL
Adolescents 12 through 18*	over 5	65 mg	½	1	1 mL
Children over 3 through 12	over 5	65 mg	½	1	1 mL
Children over 1 month through 3 years	over 5	32 mg	Use solution	½	0.5 mL
Infants birth through 1 month	over 5	16 mg	Use solution	Use solution	0.25 mL

*FDA: adolescents approaching adult size (over 150 lbs or 70 kg) should receive the full adult dose. CDC's dose figures differ in one cell: it lists ¼ of a 65 mg tablet for newborns where FDA says to use the solution. CDC also writes thresholds as "at or above" rather than "over". Follow the instructions you are given.

Who needs extra care

Adults over 40: FDA says they should be treated only if the predicted exposure is high enough to destroy the thyroid. CDC says they should take it only when officials recommend it.
Newborns and pregnant women: FDA does not recommend repeat dosing unless other protective measures are not available. CDC says infants under one month who receive more than one dose may have later developmental problems, and may need medical follow-up.
Iodine sensitivity and some conditions: FDA says people with known iodine sensitivity, dermatitis herpetiformis or hypocomplementemic vasculitis should avoid KI. People with a nodular thyroid and heart disease should not take it. People with multinodular goiter, Graves' disease or autoimmune thyroiditis should use caution. FDA adds that a seafood or shellfish allergy does not necessarily mean iodine sensitivity.
Breastfeeding: CDC notes radioactive iodine can pass to infants through breast milk, and says to consider temporarily stopping breastfeeding until evacuated from the impacted area, if possible, and to feed your baby safely in other ways.

Safety warnings

FDA: a higher dose, or taking it more often than recommended, does not offer more protection and can cause severe illness or death.
CDC: do not use table salt or foods that contain iodine as a substitute, and avoid iodine dietary supplements.
CDC: use only FDA-approved KI products.

FDA-approved products

FDA's page, current as of March 2022, lists these over-the-counter products: iOSAT tablets (130 mg and 65 mg), ThyroSafe tablets (65 mg), and Potassium Iodide Oral Solution USP (65 mg/mL). Check FDA's page for the current list and follow the label for storage and expiration dates.

Should you keep KI at home? FDA says it has not made specific recommendations for individual purchase or use, and notes that the NRC supplies tablets to states that request them for people within the 10-mile zone around a plant. If you live near a plant, ask your state or county emergency management office what their plan is. In every scenario the first step stays the same: get inside, stay inside, stay tuned.