Quick facts
- What it doesSaturates the thyroid with stable iodine so radioactive iodine-131 passes through instead of lodging
- What it does not doNothing against gamma, cesium, strontium or fallout dust; it is not a radiation pill
- Adult dose130 mg once every 24 hours, only while officials say exposure continues
- Children3 to 18 years: 65 mg; 1 month to 3 years: 32 mg; newborns: 16 mg, one dose only
- TimingWithin a few hours before or after exposure; still about half as useful at 8 hours, little use after a day
- Who benefits most
- Children
- teens
- pregnant and nursing women
- adults under 40
Potassium iodide is the most misunderstood item in a nuclear kit. People buy it thinking it is a radiation pill. It is not. It protects one gland from one isotope for one day per dose, and it does that job very well, especially for children. Everything else about surviving fallout is distance, shielding and time, which is the nuclear radiation protection page. This page is the tablets: what they do, the dose by age, when to take them, and how to keep a bottle good for a decade.
How it works
The thyroid runs on iodine and hoards it. It cannot tell stable iodine-127 from radioactive iodine-131, so after a release it soaks up whichever arrives, and iodine-131 lodged in the gland irradiates it from inside for weeks. That is how children downwind of Chernobyl got thyroid cancer, mostly through milk from cows on contaminated grass. A large dose of stable iodine taken at the right time fills the gland; it has no room left, and the radioactive iodine passes through and is gone. Iodine-131 has an eight day half-life, so the danger is over in weeks, which is why KI is a days-long measure and not a lifestyle.
Doses by age
| Who | Dose | From a 130 mg tablet | From a 65 mg tablet |
|---|---|---|---|
| Adults, and teens over about 150 lb | 130 mg | 1 tablet | 2 tablets |
| Children and teens, 3 to 18 years | 65 mg | Half a tablet | 1 tablet |
| 1 month to 3 years | 32 mg | Quarter tablet | Half a tablet |
| Newborns, birth to 1 month | 16 mg | Eighth of a tablet | Quarter tablet |
| Pregnant or nursing | 130 mg | 1 tablet, one dose only unless told otherwise | 2 tablets |
Crush a partial dose and stir it into water, juice, milk or applesauce; it tastes salty and bitter, and a spoon of jam hides it for a child. One dose covers 24 hours. Repeat only while officials say exposure continues. Newborns and nursing mothers get one dose because repeated KI suppresses an infant's thyroid, and a newborn who gets a dose should have a thyroid check afterward.
Taken within a few hours before or after the plume arrives, KI blocks nearly all uptake. At 8 hours after exposure it blocks about half. After 24 hours it does almost nothing and can hold radioactive iodine that is already in the gland. So the bottle lives where you can reach it in minutes, and the trigger is the official word, a siren, or an alert on the phone, not a rumor. Taking it early for no reason is not free: side effects include rash, upset stomach, swollen glands and, with repeated doses, a suppressed or overactive thyroid.
Who it is really for
Do not take it: known iodine allergy, dermatitis herpetiformis, hypocomplementemic vasculitis. Take it only on official instruction and watch for a reaction: Graves' disease, multinodular goiter, autoimmune thyroiditis. Iodine in shellfish or contrast dye is a different thing from an iodine allergy; ask a doctor now, not on the day.
Storage and shelf life
Potassium iodide is a simple, stable salt. Kept dry in its foil, a tablet is good far past the printed date; the same tablets in government stockpiles have had their dates extended again and again after testing. A tablet that has gone yellow or brown has taken on moisture and iodine is escaping, so that bottle gets replaced. The rules:
- Original blister or bottle, sealed, in a zip bag with a desiccant
- Cool and dark: a bedroom drawer, the medical kit, the go-bag, not a vehicle
- One bottle per household location, plus the vehicle kit if you drive far from home
- Count: 14 adult doses per person covers two weeks, far longer than any event has needed
- Write the dose card from the table above and tape it to the bottle
What I keep
MIRA Safety potassium iodide tablets
65 mg tablets; adults take two, children 3 to 18 take oneIndividually sealed tablets with a long date. The 65 mg size makes the child's dose a whole tablet instead of a split, which matters at two in the morning with a scared kid. Two tablets is the adult 130 mg.
Potassium iodide as a Jase Case add-on
Ships with the emergency antibiotic kitIf you are ordering the Jase Case anyway, KI is one of the add-ons and it arrives in the same box, which keeps the whole emergency medication supply in one place.
Lugol's solution is a different tool. The Lugol's iodine page covers what it is for on this site; the dose math from drops to milligrams is too easy to get wrong to plan around it for a fallout event.
Questions this answers
Tap a question for the short answer.
What do potassium iodide tablets do?
They load the thyroid with ordinary, stable iodine. The thyroid cannot tell stable iodine from the radioactive iodine-131 that a reactor accident or a nuclear detonation puts into the air, milk and water, and it grabs whichever arrives first. A full thyroid has no room for the radioactive kind, so it passes through and out. That is the entire effect: thyroid cancer prevention, mostly in children. KI does nothing for the rest of the body and nothing against any other radioactive element.
When should I take potassium iodide?
When officials say a release of radioactive iodine is coming or has happened, and not before. Taken within a few hours before or after exposure it blocks nearly all uptake; at 8 hours after it still blocks about half; after 24 hours it does little and can even trap iodine already absorbed. One dose covers 24 hours. Repeat only while exposure continues, which for most events is a few days, not weeks. Nobody takes it as a precaution when nothing has happened; the side effects are real and the benefit is zero.
How long does one dose of potassium iodide protect you?
About 24 hours. Take the next dose only if officials say radioactive iodine is still in the air or the food supply. Pregnant and nursing women and newborns should get a single dose unless told otherwise, because repeated doses suppress the baby's thyroid.
How long do potassium iodide tablets last in storage?
Effectively forever if they stay dry and sealed. KI is a stable salt; the printed date is a conservative label, and government stockpiles have had their shelf lives extended repeatedly after testing. Tablets that are dry, white and intact in their foil are good. Yellow or brown tablets have taken on moisture and are the ones to replace. Cool, dry, sealed in the original blister, and they are a ten year item.
Does potassium iodide protect against all radiation?
No. It protects one organ, the thyroid, from one isotope, iodine-131. It does nothing against gamma radiation from fallout, nothing against cesium-137 or strontium-90, and nothing about breathing fallout dust. Distance, shielding and time do that work: get inside, get to the middle or the basement, stay there. KI is one small piece of the plan on the nuclear radiation page, not the plan.
Can I use lugol's iodine instead of potassium iodide?
Not as a planned substitute. The tablets deliver an exact 130 or 65 mg dose; Lugol's solution varies by strength and the drops-to-milligrams math is easy to get wrong by a factor of two or more, in either direction. Lugol's is on the shelf here for the jobs the compound page lists. For the thyroid in a fallout event, buy the tablets; they cost less than a tank of gas for a family and keep for a decade.
How much potassium iodide should a child take?
Ages 3 to 18: 65 mg, which is half of the adult 130 mg tablet, or a whole 65 mg tablet. A teenager who is adult size, about 150 lb, takes the adult 130 mg. One month to 3 years: 32 mg, a quarter of a 130 mg tablet, crushed in water, juice or milk. Newborns under one month: 16 mg, an eighth of a tablet, one dose only. Children are the reason KI exists; their thyroids take up iodine fastest and their cancer risk from it is highest.
Who should not take potassium iodide?
Anyone with a known iodine allergy, and people with the rare skin condition dermatitis herpetiformis or hypocomplementemic vasculitis. People with thyroid disease, especially Graves' disease or a multinodular goiter, and anyone over 40 should take it only if officials call for it, because their cancer risk from iodine-131 is small and their risk of a thyroid reaction to the tablet is higher. Over 40, the risk of harm from the pill roughly matches the risk it prevents, so it is a judgment call made on the day.
Keep going
Related to this
Membership · $49.95 per year
There is a lot more behind the lock
Every recipe and resource from the Prepper's Chemical Survival Guide, all six field guides to read here and download, the full audit and logbook, all twelve reference charts, and no ads.
My Manual · included
Build your own field manual
The most useful thing a membership gives you. Save any page on this site, recipes, charts, and whole field guides included. Arrange them in the order you want, name it, and print one manual with a cover and contents, or keep it as a PDF that opens with no signal.
- It works when this site does not
- Only your pages
- Anyone in the house can use it
- One current copy, not a pile of printouts
- The house binder
- A copy for the bug-out bag or truck
- A copy for family
- An offline PDF
Stay Ready
New entries, updates, and useful instruction.
Stay one step ahead on your preparedness journey.
