Home Ingredients Potassium Iodide (KI)
Thyroid Health

Potassium Iodide (KI)

Evidence Level
Moderate
1 Clinical Trial
2 Documented Benefits
3/5 Evidence Score

Potassium iodide (KI) is a common inorganic form of iodine, the mineral the thyroid needs to make thyroid hormone. As a nutrient it supplies the iodine in many supplements, often 150 mcg, is almost completely absorbed, and is one of the forms the FDA allows for iodizing salt. The American Thyroid Association advises a 150 mcg potassium iodide supplement before and during pregnancy and breastfeeding, although a large trial in mildly deficient pregnant women found no effect on child development. Separately, at doses hundreds of times higher and only when public health officials direct it, KI is used to block radioactive iodine uptake by the thyroid in a nuclear emergency; that is a medical use, not a benefit of daily supplements. Unlike kelp, KI has a known iodine content.

Studied Dose Nutritional: 150 mcg iodine a day (adult RDA); the pregnancy trial used 200 mcg a day. The 130 mg adult KI dose for a nuclear emergency is over 600 times the RDA and is taken only when public health officials direct it.
Active Compound Potassium iodide (KI)

Benefits

Supports adequate iodine for thyroid hormone production

Potassium iodide supplies iodide, which the thyroid uses to make thyroid hormone, and it is the form the American Thyroid Association advises as a 150 mcg supplement before and during pregnancy and breastfeeding. Iodine deficiency is the most common cause of preventable mental impairment worldwide. Where mild deficiency has left autonomous thyroid nodules, raising iodine intake brings a transient rise in hyperthyroidism.

Supported by Trial 1

Known iodine content per dose

Kelp-derived iodine is unreliable: a market survey found seaweed supplements supplying anywhere from 5 to 5,600 micrograms of iodine per daily dose, and a case report of possible arsenic toxicosis from a kelp supplement went on to find arsenic above the FDA tolerance level in eight of nine kelp products tested. Potassium iodide has a defined iodine content and is absorbed almost completely.

Supported by Trial 1

Mechanism of action

1

Thyroid iodine uptake

The thyroid concentrates iodide through the sodium-iodide symporter (NIS) to make thyroid hormone; T3 and T4 contain 3 and 4 iodine atoms. Severe iodine deficiency leads to goiter and hypothyroidism.

2

Wolff-Chaikoff effect (high-dose iodine)

A large iodide load briefly blocks thyroid hormone synthesis. Most people escape this effect within a few days, but some, including people with autoimmune thyroiditis, newborns and fetuses, do not and can become hypothyroid. Raising iodine intake in people with autonomous thyroid nodules can cause iodine-induced hyperthyroidism.

3

Radioactive iodine blocking

Stable potassium iodide floods the thyroid with non-radioactive iodide so that less radioactive iodine-131 is taken up. Taken within 1 to 2 hours of inhaling radioiodine it blocks more than 90 percent of thyroid uptake, protection lasts about 24 hours, and modelling suggests little benefit once 16 hours or more have passed since exposure.

Clinical trials

1
Iodine in pregnancy and child development (RCT)
PubMed

Randomized, double-blind, placebo-controlled trial of 200 mcg iodine a day or placebo from early pregnancy until delivery, with child IQ and executive function tested at age 5 to 6. (Gowachirapant et al. 2017, Lancet Diabetes Endocrinol)

832 mildly iodine-deficient pregnant women in Bangalore, India and Bangkok, Thailand (median urinary iodine 131 mcg/L); about 315 children were assessed.

No effect on any co-primary outcome: verbal IQ 89.5 versus 90.2, performance IQ 97.5 versus 99.1, and executive function score 90.6 versus 91.5. Adverse events did not differ between groups. The trial reports the dose as iodine without naming the chemical form used.

Side effects and drug interactions

Common Potential side effects

Acute iodine poisoning is rare and usually needs doses of many grams; symptoms include burning of the mouth, throat and stomach, nausea, vomiting and diarrhea.
Iodine-induced hyperthyroidism, particularly where long-standing mild deficiency has left autonomous thyroid nodules.
Iodine-induced hypothyroidism, particularly in people with autoimmune thyroiditis, who may not escape the thyroid-blocking effect of a large iodide load.
Pregnancy: large iodide doses can cause hypothyroidism in the fetus, which may not escape the thyroid-blocking effect.

Important Drug interactions

ACE inhibitors and potassium-sparing diuretics: taking potassium iodide with them can raise the risk of high blood potassium (hyperkalemia).
Antithyroid drugs such as methimazole: high doses of iodine can add to their effect and could cause hypothyroidism.

Featured in these supplement guides

Thyroid Support→

More Thyroid Health Ingredients

Thyroid Health
Iodine
Iodine is an essential trace mineral that the thyroid uses to make thyroid hormones, which…
Thyroid Health
Kelp / Seaweed Iodine (Laminaria, Ascophyllum, Wakame)
Kelp and other brown seaweeds (Laminaria, Ascophyllum nodosum or knotted wrack, Undaria or…
Thyroid Health
SelenoForce® (Selenium-Enriched Yeast — Sabinsa)
SelenoForce® is Sabinsa's branded selenium-enriched Saccharomyces cerevisiae yeast — a foo…
Thyroid Health
IodAid™ (organic brown-seaweed iodine — InnoVactiv)
IodAid is an ingredient from InnoVactiv, a company in Rimouski, Quebec, made by concentrat…

Explore Other Ingredients

Antioxidant
Selenium
Selenium is an essential trace mineral built into about 25 selenoproteins, including antio…
Immune Support
Zinc
Zinc is an essential trace mineral that hundreds of enzymes need, and it plays a role in i…
Bone Health
Vitamin D
Vitamin D is a fat-soluble vitamin the body turns into a hormone that controls calcium abs…

Frequently asked questions about Potassium Iodide (KI)

What is potassium iodide used for?

Potassium iodide (KI) is a source of iodine, the mineral needed to make thyroid hormones. In small amounts it supports thyroid function; in high pharmaceutical doses it is used to protect the thyroid during radiation emergencies.

How much potassium iodide should I take?

For nutritional iodine the adult requirement is 150 mcg a day, and many multivitamins provide about 150 mcg. Some iodine-only supplements contain much higher doses, sometimes above the 1,100 mcg daily upper limit. The 130 mg tablets used in radiation emergencies are a separate, medically directed use, not for daily supplementation.

Can you take too much potassium iodide?

Yes. Excess iodine can disrupt the thyroid, causing either underactive or overactive function in susceptible people. Stay near the recommended nutritional amount unless a doctor directs otherwise; do not take high-dose KI without medical guidance.

What is the difference between potassium iodide and other iodine supplements?

Potassium iodide is one common chemical form used to deliver iodine; other supplements use kelp, sodium iodide, or molecular iodine. They all supply iodine, with the key being the total iodine amount rather than the specific salt.

What is Potassium Iodide?

Potassium iodide (KI) is a common inorganic form of iodine, the mineral the thyroid needs to make thyroid hormone. As a nutrient it supplies the iodine in many supplements, often 150 mcg, is almost completely absorbed, and is one of the forms the FDA allows for iodizing salt.

Is Potassium Iodide safe, and does it have side effects?

Side effects and cautions reported for Potassium Iodide include: Acute iodine poisoning is rare and usually needs doses of many grams; symptoms include burning of the mouth, throat and stomach, nausea, vomiting and diarrhea. Iodine-induced hyperthyroidism, particularly where long-standing mild deficiency has left autonomous thyroid nodules. It may also interact with some medications. Potassium Iodide is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does Potassium Iodide interact with any medications?

Possible interactions include: ACE inhibitors and potassium-sparing diuretics: taking potassium iodide with them can raise the risk of high blood potassium (hyperkalemia). Antithyroid drugs such as methimazole: high doses of iodine can add to their effect and could cause hypothyroidism. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Potassium Iodide?

NutraSmarts rates the evidence for Potassium Iodide as Moderate (3 out of 5). It is backed by 1 study summary and 10 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(10 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Leung AM, Bauer AJ, Benvenga S, Brenner AV, Hennessey JV, Hurley JR, Milan SA, Schneider AB, Sundaram K, Toft DJ. American Thyroid Association Scientific Statement on the Use of Potassium Iodide Ingestion in a Nuclear Emergency. Thyroid. 2017;27(7):865-877. doi: 10.1089/thy.2017.0054.PubMedUsed to support: American Thyroid Association statement on KI in a nuclear emergency. The full text (PMC5561443) reports that KI taken within 1 to 2 hours of inhaling radioiodine blocks more than 90 percent of thyroid uptake, that protection lasts about 24 hours, the FDA dosing table (130 mg for adults), and that Poland gave about 17.5 million doses after Chernobyl and none of the more than 6000 later thyroid cancers in people exposed as children arose there.
  2. Becker DV, Zanzonico P. Potassium iodide for thyroid blockade in a reactor accident: administrative policies that govern its use. Thyroid. 1997;7(2):193-7. doi: 10.1089/thy.1997.7.193.PubMedUsed to support: Reviews the Chernobyl experience: Poland distributed KI to ~16 million people with rare side effects and an estimated ~40% reduction in projected thyroid dose; argues for KI stockpiling and explains the radioiodine-blockade rationale (saturation of iodide uptake).
  3. Zimmermann MB, Boelaert K. Iodine deficiency and thyroid disorders. Lancet Diabetes Endocrinol. 2015;3(4):286-95. doi: 10.1016/S2213-8587(14)70225-6.PubMedUsed to support: Review of iodine deficiency and thyroid disorders: severe deficiency causes goitre and hypothyroidism; mild-to-moderate deficiency raises the prevalence of toxic nodular goitre and hyperthyroidism, which rises further, transiently, when iodine intake is increased by salt iodisation.
  4. Markou K, Georgopoulos N, Kyriazopoulou V, Vagenakis AG. Iodine-Induced hypothyroidism. Thyroid. 2001;11(5):501-10. doi: 10.1089/105072501300176462.PubMedUsed to support: Reviews the acute Wolff-Chaikoff effect and iodine-induced hypothyroidism: large iodide loads (as in high-dose KI) acutely inhibit thyroid hormone synthesis; most healthy thyroids escape, but failure to escape (autoimmune thyroid disease, fetuses/neonates) can cause hypothyroidism; this is the key high-dose-iodide caution.
  5. Gowachirapant S, Jaiswal N, Melse-Boonstra A, Galetti V, Stinca S, Mackenzie I, Thomas S, Thomas T, Winichagoon P, Srinivasan K, Zimmermann MB. Effect of iodine supplementation in pregnant women on child neurodevelopment: a randomised, double-blind, placebo-controlled trial. Lancet Diabetes Endocrinol. 2017;5(11):853-863. doi: 10.1016/S2213-8587(17)30332-7.PubMedUsed to support: Randomised, double-blind, placebo-controlled trial of 200 mcg oral iodine daily in 832 mildly iodine-deficient pregnant women in Bangalore, India and Bangkok, Thailand. Child verbal IQ (89.5 versus 90.2), performance IQ (97.5 versus 99.1) and executive function (90.6 versus 91.5) at age 5 to 6 did not differ from placebo.
  6. Amster E, Tiwary A, Schenker MB. Case report: potential arsenic toxicosis secondary to herbal kelp supplement. Environ Health Perspect. 2007;115(4):606-8. doi: 10.1289/ehp.9495.PubMedUsed to support: A woman with alopecia, memory loss, rash, fatigue and vomiting had a urine arsenic of 83.6 micrograms per gram creatinine against a normal below 50, and her kelp supplement contained 8.5 ppm arsenic; symptoms and levels resolved after she stopped taking it. The authors then analysed nine kelp products bought from health food stores and found eight of the nine above the FDA tolerance level of 0.5 to 2 ppm for certain foods.
  7. Zimmermann MB, Jooste PL, Pandav CS. Iodine-deficiency disorders. Lancet. 2008;372(9645):1251-62. doi: 10.1016/S0140-6736(08)61005-3.PubMedUsed to support: Lancet seminar: about 2 billion people have insufficient iodine intake; deficiency is the most common cause of preventable mental impairment worldwide; salt iodization is the best control strategy in nearly all countries, and introducing it may transiently increase thyroid disorders.
  8. Zanzonico PB, Becker DV. Effects of time of administration and dietary iodine levels on potassium iodide (KI) blockade of thyroid irradiation by 131I from radioactive fallout. Health Phys. 2000;78(6):660-7. doi: 10.1097/00004032-200006000-00008.PubMedUsed to support: Computer-modelling study of KI timing: in iodine-sufficient adults, KI given up to 48 hours before 131I exposure almost completely blocks thyroid uptake, while KI given afterwards has a smaller, rapidly falling effect (about 80% protection at 2 hours and 40% at 8 hours), and KI taken 16 hours or later after exposure has little or no protective effect.
  9. Aakre I, Solli DD, Markhus MW, Mæhre HK, Dahl L, Henjum S, Alexander J, Korneliussen PA, Madsen L, Kjellevold M. Commercially available kelp and seaweed products - valuable iodine source or risk of excess intake? Food Nutr Res. 2021;65. doi: 10.29219/fnr.v65.7584.PubMedUsed to support: ICP-MS analysis of 96 macroalgae products on the Norwegian market: the 14 dietary supplements containing macroalgae supplied 5 to 5,600 micrograms of iodine per daily dose, species and iodine labelling was inadequate or inaccurate for several products, and the authors call macroalgae products unreliable iodine sources.
  10. Office of Dietary Supplements, National Institutes of Health. Iodine: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. 2024;Updated November 5, 2024..SourceUsed to support: Not PubMed-indexed (US government fact sheet). Supplements often supply iodine as potassium iodide, which is absorbed almost completely (96.4 percent); many multivitamins contain 150 mcg and some iodine-only supplements exceed the 1,100 mcg adult upper limit; FDA allows potassium iodide for salt iodization; the American Thyroid Association advises 150 mcg a day of potassium iodide before and during pregnancy and lactation; acute poisoning needs doses of many grams; potassium iodide with ACE inhibitors or potassium-sparing diuretics can raise hyperkalemia risk, and high-dose iodine with antithyroid drugs can be additive.