← All supplements
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.

Where to buy

View on iHerb

Ships to 180+ countries · welcome discount for new customers

Referral link — this site may earn a commission on purchases.

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.

How to take it

TimingTiming does not matter for the 150 mcg nutritional dose.
With food?Take it with food if it causes a metallic taste or stomach upset, otherwise it makes no difference.
Worth knowingIf you already use iodised salt and eat dairy or fish regularly, you are probably meeting the requirement without a supplement.

Interactions

With medications

  • lithium

    Lithium and iodine both suppress thyroid hormone release, and together they more readily cause hypothyroidism and goitre. do not combine without thyroid function monitoring

  • antithyroid drugs (methimazole, carbimazole, propylthiouracil)

    Additive suppression of thyroid hormone production can tip you into hypothyroidism. do not combine without medical supervision

  • amiodarone

    Amiodarone is already a very large iodine load, and added iodine increases the risk of thyroid dysfunction. avoid iodine supplements unless your doctor directs otherwise

  • potassium-sparing diuretics and ACE inhibitors

    Relevant only for the 130 mg emergency tablets, where the potassium content adds to serum potassium. follow public health instructions and tell your doctor if you take these drugs

With other supplements

  • kelp, bladderwrack and other seaweed products

    Seaweeds carry unlabelled and highly variable iodine, so combined intake can reach milligram levels. do not stack iodine sources; use one product with a stated dose

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Should you take potassium iodide as a daily iodine supplement?

Only if your iodine intake is low; the nutritional need is 150 mcg/day (250 mcg in pregnancy and lactation). If you use iodised salt and eat dairy or fish regularly, you probably meet it without potassium iodide.

Does potassium iodide protect against radiation?

Potassium iodide blocks thyroid uptake of radioactive iodine and is recommended by the American Thyroid Association and WHO for radiation emergencies, but the direct evidence is limited: four observational studies of low to very low quality. The emergency dose is 130 mg for adults, taken once, only when public health authorities instruct.

Can too much potassium iodide harm your thyroid?

Yes. High-dose iodine from potassium iodide can trigger hyperthyroidism in people with nodular goitre and hypothyroidism in people with autoimmune thyroiditis, so avoid excess if you have Hashimoto's or Graves' disease. Do not take emergency-dose tablets prophylactically.

Can you take potassium iodide with kelp supplements?

Do not stack them: kelp and other seaweed products carry unlabelled, highly variable iodine, so combined with potassium iodide your intake can reach milligram levels. Use one product with a stated dose.

Scientific references

Related in Vitamins & minerals