Moderate evidenceVitamins & minerals

Potassium Iodide

An iodine salt used to correct iodine deficiency and, at high dose, to block the thyroid after a radioactive iodine release. The emergency use is guideline-backed but rests on thin direct evidence, and the everyday supplement case applies only where intake is low.

Evidence last reviewed: August 2026

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What the science says

Correcting iodine deficiency Moderate evidence
A systematic review and meta-analysis of 14 trials found iodine supplementation in pregnancy improves iodine status and prevents the rise in thyroglobulin. The same analysis found no improvement in birth size or in infants' cognitive, language or motor development in the first two years.
Thyroid blocking after a nuclear accident Limited evidence
A systematic review found only four observational studies of iodine blocking after nuclear accidents, giving low to very low quality evidence that potassium iodide reduced thyroid cancer risk in children, with no data on hypothyroidism or nodules.
Recommended despite the thin evidence Limited evidence
The American Thyroid Association and WHO recommend stockpiling and timely administration of potassium iodide in a radiation emergency, based on the well-understood mechanism of saturating thyroid iodine uptake rather than on randomized data — which could never ethically be collected.

Dosage & safety

Studied doseNutritional needs are 150 µg/day of iodine (250 µg in pregnancy and lactation); most supplements provide 150 µg. The emergency thyroid-blocking dose is entirely different — 130 mg for adults, taken once, only when public health authorities instruct.

SafetyHigh-dose iodine can both cause and worsen thyroid disease: it can trigger hyperthyroidism in people with nodular goitre and hypothyroidism in people with autoimmune thyroiditis. Kelp and "thyroid support" products often deliver milligram doses without saying so. Avoid excess in pregnancy, in Hashimoto's or Graves' disease, and with lithium or antithyroid drugs. Do not take emergency-dose tablets prophylactically.

Scientific references

Effects of iodine supplementation during pregnancy on pregnant women and their offspring: a systematic review and meta-analysis of trials over the past 3 decades
Nazeri P, Shariat M, Azizi F — Eur J Endocrinol, 2021
The effects of iodine blocking on thyroid cancer, hypothyroidism and benign thyroid nodules following nuclear accidents: a systematic review
Pfinder M, Dreger S, Christianson L — J Radiol Prot, 2016
American Thyroid Association Scientific Statement on the Use of Potassium Iodide Ingestion in a Nuclear Emergency
Leung AM, Bauer AJ, Benvenga S — Thyroid, 2017

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