Potassium Iodide (KI) Dosage Guide: FDA-Approved Doses by Age and Weight
Adult dose (18–40 years): 130 mg KI — one tablet, taken once every 24 hours only while radioactive iodine exposure risk persists. Children 3–18 years: 65 mg. Infants 1 month–3 years: 32 mg. Newborns: 16 mg. Adults over 40: take only if projected thyroid dose ≥ 500 cGy.
⚠️ Safety warning: KI protects ONLY the thyroid from radioactive iodine. It does NOT protect against other radiation types. Take ONLY on instruction from public health authorities.What this guide covers: This reference article provides the complete FDA-approved potassium iodide (KI) dosage table for all age groups, explains the mechanism of thyroid blocking, identifies who should and should not take KI, and answers the most common questions about timing, duration, and safety. All data is sourced from the FDA Potassium Iodide guidance, the CDC Radiation Emergencies resource, and the WHO Iodine Thyroid Blocking guidelines.
Table of Contents
What Is Potassium Iodide and How Does It Work?
Potassium iodide (KI) is a stable (non-radioactive) salt of iodine. In a nuclear emergency, radioactive iodine-131 (I-131) is released into the atmosphere and can be inhaled or ingested through contaminated food and water. The thyroid gland preferentially absorbs iodine — both stable and radioactive — to produce thyroid hormones.
When you take KI before or shortly after exposure, the thyroid becomes saturated with stable iodine. This saturation prevents the thyroid from absorbing radioactive I-131, thereby reducing the risk of radiation-induced thyroid cancer — a well-documented consequence of nuclear fallout, as observed after the Chernobyl accident in 1986 and the Fukushima Daiichi incident in 2011.
Critical limitation: KI is a single-purpose drug. It protects only the thyroid gland, and only from radioactive iodine. It provides zero protection against external gamma radiation, cesium-137, strontium-90, plutonium, or any other radioactive isotope. Shelter-in-place and evacuation remain the primary protective actions in any nuclear emergency.
FDA-Approved Dosage Table (All Age Groups)
The following table reflects the official FDA guidance on potassium iodide dosing, published in the Guidance: Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies (FDA, 2001, updated 2023). Doses are given as a single daily dose, repeated every 24 hours only while the risk of radioactive iodine exposure persists.
| Age Group | KI Dose | Thyroid Dose Threshold | Form | Notes |
|---|---|---|---|---|
| Adults 18–40 years | 130 mg | ≥ 10 cGy projected thyroid dose | 1 × 130 mg tablet | Standard adult dose. Highest thyroid cancer risk from I-131. |
| Adults > 40 years | 130 mg | ≥ 500 cGy projected thyroid dose | 1 × 130 mg tablet | Higher threshold: thyroid cancer risk lower, iodine side effects higher in older adults. |
| Pregnant and breastfeeding women | 130 mg | ≥ 5 cGy projected thyroid dose | 1 × 130 mg tablet | Lowest threshold. Fetal thyroid is highly sensitive. Repeat dosing requires medical supervision. |
| Adolescents 12–18 years (< 68 kg) | 65 mg | ≥ 5 cGy projected thyroid dose | ½ × 130 mg tablet or 65 mg tablet | If adolescent weighs ≥ 68 kg (150 lbs), use adult dose of 130 mg. |
| Children 3–12 years | 65 mg | ≥ 5 cGy projected thyroid dose | ½ × 130 mg tablet or liquid | Can crush tablet and mix with juice, milk, or water. |
| Infants 1 month–3 years | 32 mg | ≥ 5 cGy projected thyroid dose | Liquid formulation recommended | ¼ × 130 mg tablet dissolved in liquid. Liquid KI solution preferred. |
| Newborns (birth–1 month) | 16 mg | ≥ 5 cGy projected thyroid dose | Liquid only | Lowest dose. Neonatal thyroid is extremely sensitive. Monitor for hypothyroidism after dosing. |
Source: FDA Guidance: Potassium Iodide as a Thyroid Blocking Agent (2001, updated 2023). cGy = centigray, a unit of absorbed radiation dose.
Weight Threshold for Adolescents: The 68 kg Rule
The FDA applies a body-weight threshold for adolescents aged 12–18 years. An adolescent who weighs 68 kg (150 lbs) or more should receive the full adult dose of 130 mg, not the reduced 65 mg dose. This is because thyroid iodine uptake scales with body mass, and a heavier adolescent requires the same saturation dose as an adult to achieve full thyroid blocking.
For children under 12, the dose is fixed at 65 mg regardless of weight, as the pediatric thyroid is smaller and saturates at a lower dose. For infants and newborns, liquid formulations are strongly preferred over crushed tablets, as precise dosing is critical at these low levels.
When to Take KI — and When NOT to Take It
✅ TAKE KI when:
- Public health authorities or emergency management officials issue a specific directive to take KI
- You are within the Emergency Planning Zone (EPZ) of a nuclear power plant and an accident has been declared
- A nuclear detonation has occurred and you are in or downwind of the fallout zone
- You are pregnant, breastfeeding, or have children under 18 in your household
- You have been told the projected thyroid dose meets or exceeds the threshold for your age group
❌ DO NOT take KI if:
- No official directive has been issued — unsanctioned use provides no benefit and risks side effects
- You have a known allergy to iodine or shellfish (consult a physician)
- You have hyperthyroidism (overactive thyroid) — iodine can trigger thyroid storm
- You have thyroid nodules, Graves' disease, or autoimmune thyroid disease without medical guidance
- You are over 40 and the projected dose is below 500 cGy — risk of side effects outweighs benefit
- You have dermatitis herpetiformis or hypocomplementemic vasculitis
⚠️ Do not use table salt or iodized food salt as a substitute for KI. The iodine content in table salt is far too low to provide thyroid blocking — you would need to consume a toxic quantity of salt to approach the required iodine dose. Only pharmaceutical-grade potassium iodide (KI) tablets or solution should be used.
Timing: How Early Before Exposure Should You Take KI?
The effectiveness of KI depends critically on timing. According to the FDA and WHO, the optimal window for taking KI is within 1–4 hours before anticipated exposure to radioactive iodine. Taking KI too early or too late significantly reduces its protective effect:
| Timing Relative to Exposure | Thyroid Protection Achieved | Recommendation |
|---|---|---|
| 1–4 hours before exposure | ~100% blockage | Optimal window — take as soon as directive is issued |
| At time of exposure | ~90% blockage | Still highly effective — take immediately if directive received |
| 2–4 hours after exposure | ~50% blockage | Partial benefit — still recommended if within 4 hours |
| 8 hours after exposure | ~10% blockage | Minimal benefit — consult health authorities |
| > 24 hours after exposure | Negligible | Not recommended — radioactive iodine already absorbed |
Source: WHO Iodine Thyroid Blocking: Guidelines for Use in Planning and Responding to Radiological and Nuclear Emergencies (2017).
How Long to Continue Taking KI
A single dose of KI provides thyroid protection for approximately 24 hours. If radioactive iodine exposure risk continues beyond 24 hours — as may occur during a prolonged nuclear accident or multi-day fallout event — the dose may be repeated every 24 hours, but only under the direction of public health authorities.
The FDA and WHO generally recommend against self-administering more than a few doses without medical oversight, particularly for newborns, infants, pregnant women, and individuals over 40. Repeated high doses of iodine can cause iodine-induced thyroid dysfunction (both hypo- and hyperthyroidism), particularly in vulnerable populations.
Practical note: In most radiological emergency scenarios, the period of significant radioactive iodine release is relatively short (hours to a few days). Evacuation or sheltering-in-place typically reduces exposure duration. KI is a short-term protective measure, not a long-term treatment.
Side Effects and Contraindications
When taken at the correct dose, KI is generally well tolerated by healthy individuals. The most common side effects are gastrointestinal: nausea, stomach upset, and a metallic or bitter taste. These can be minimized by taking KI with food, milk, or a large glass of water.
More serious adverse effects are rare but include:
- Iodism: Symptoms of iodine excess including burning in the mouth, metallic taste, sore teeth and gums, and skin rash. Typically resolves when KI is discontinued.
- Thyroid dysfunction: Both hypothyroidism and hyperthyroidism can be triggered by iodine loading, particularly in individuals with pre-existing thyroid conditions or in newborns. The Wolff-Chaikoff effect (transient hypothyroidism from iodine excess) is the primary concern in neonates.
- Allergic reactions: Rare but can include hives, swelling, or difficulty breathing. Seek emergency medical care immediately.
- Sialadenitis: Swelling of the salivary glands — uncommon at standard doses.
Individuals with the following conditions should consult a physician before taking KI: hyperthyroidism, hypothyroidism, thyroid nodules, Graves' disease, Hashimoto's thyroiditis, dermatitis herpetiformis, hypocomplementemic vasculitis, or known iodine hypersensitivity.
Calculate Your Family's Full Emergency Supply Needs
KI tablets are just one component of a complete nuclear preparedness kit. Use our free Fallout Shelter Supply Calculator to determine exact water, food, and supply quantities for your household based on FEMA guidelines.
Open Fallout Shelter Calculator →Frequently Asked Questions
A single dose of KI provides thyroid protection for approximately 24 hours. The iodide ion has a biological half-life of roughly 10–14 hours in the thyroid gland. For continued radioactive iodine exposure, the FDA recommends repeating the dose every 24 hours, but only while the risk persists and under direction of public health authorities. KI does not accumulate in other tissues in a clinically significant way at standard doses.
The FDA-approved adult dose of KI is 130 mg for adults aged 18–40 years. Adults over 40 should only take KI if the projected thyroid dose exceeds 500 cGy. One standard 130 mg tablet equals one dose. Do not take more than one tablet per dose — higher doses do not increase protection and increase the risk of side effects.
Yes. Exceeding the recommended dose does not increase thyroid protection — the thyroid saturates at the correct dose. Overdose can cause iodine toxicity symptoms including nausea, vomiting, burning in the mouth, and in severe cases, thyroid dysfunction. Never take more than the FDA-recommended dose for your age group. More is not better.
People who should NOT take KI without medical supervision include: those with thyroid disease (hyperthyroidism, hypothyroidism, or thyroid nodules), those with known iodine allergy, and adults over 40 unless the projected thyroid dose exceeds 500 cGy. Dermatitis herpetiformis and hypocomplementemic vasculitis are also contraindications. Always consult a physician if you have any thyroid condition.
No. KI protects ONLY the thyroid gland from radioactive iodine (I-131). It provides no protection against external gamma radiation, cesium-137, strontium-90, or any other radioactive isotopes. Shelter-in-place and evacuation remain the primary protective actions in a nuclear emergency. KI is a supplementary measure, not a comprehensive radiation shield.
More Frequently Asked Questions
Can iodized table salt be used instead of KI pills?
No — and attempting this is dangerous. Iodized table salt contains approximately 77 micrograms (mcg) of iodine per gram. A standard 130 mg KI tablet contains 100 mg of elemental iodine. To match that dose using table salt, you would need to consume over 1.5 kg (3.3 lbs) of salt — a quantity that would cause fatal hypernatremia (sodium poisoning) long before providing any thyroid protection. Only pharmaceutical-grade potassium iodide tablets or oral solution (available from pharmacies and emergency preparedness suppliers) should be used.
How long does KI protection last?
A single dose of potassium iodide provides thyroid protection for approximately 24 hours. The iodide saturates the thyroid's uptake capacity for that period. If radioactive iodine exposure risk continues beyond 24 hours — for example, during a prolonged nuclear power plant accident — the dose may be repeated every 24 hours, but only under the direction of public health authorities. Self-administering multiple doses without guidance is not recommended, particularly for newborns, infants, pregnant women, and adults over 40.
Is KI safe for pregnant women?
Yes, under medical guidance. Pregnant women have the lowest dose threshold of any group (≥ 5 cGy projected thyroid dose) because the fetal thyroid begins concentrating iodine from approximately week 10–12 of gestation and is highly sensitive to radioactive iodine. The FDA-approved dose for pregnant women is 130 mg — the same as for other adults aged 18–40. However, repeat dosing during pregnancy requires medical supervision, as high iodine intake can suppress fetal thyroid function (Wolff-Chaikoff effect) and cause neonatal hypothyroidism. Breastfeeding mothers should also take KI, as radioactive iodine concentrates in breast milk.
Does KI protect against dirty bombs?
Only if the dirty bomb disperses radioactive iodine (I-131). In practice, most radiological dispersal devices (dirty bombs) use more readily available isotopes such as cesium-137, cobalt-60, iridium-192, or strontium-90. KI provides zero protection against these isotopes or against external gamma radiation. If authorities confirm that radioactive iodine is present in the dispersal — a less common scenario — then KI would be recommended. For all dirty bomb events, the primary protective actions are shelter-in-place, evacuation, and decontamination as directed by emergency management authorities.
References and Official Sources
- FDA — Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies (2001, updated 2023)
- CDC — Potassium Iodide (KI) for Radiation Emergencies
- WHO — Iodine Thyroid Blocking: Guidelines for Use in Planning and Responding to Radiological and Nuclear Emergencies (2017)
- NRC — Fact Sheet on Potassium Iodide
- FEMA Ready.gov — Nuclear Explosion Preparedness