Iodine (umbrella: potassium iodide, kelp / Fucus vesiculosus)

Trace element; substrate of thyroid hormone synthesis

ATC code: H03CA-IODINE

Brand names: Kelp (Nature's Way), ThyroShield, Iosat, Solgar Kelp

Updated 24 Sep 2026 · Methodology

Indications

Iodine deficiency disorders

First line

Prevention and treatment of iodine deficiency disorders: endemic goitre, deficiency hypothyroidism, childhood cretinism. 2007 and 2014 recommend universal salt iodisation and additional 150 mcg/day in adults in endemic regions. Russia and parts of Spain are moderately iodine-deficient; routine iodine prophylaxis is reasonable in Moscow, the Ural and Siberian regions and in Castile and León. AEMPS approves Yoduk and Yodocefol for this purpose. Potassium iodide is the drug of choice; iHerb kelp is unsuitable for routine prevention due to dose variability.

Sources

ICD-10: E01 · ICD-11: 5A00.1

Pregnancy and iodine

First line

Iodine deficiency prevention in pregnant and lactating women. 2014, Endocrine Society 2017, SEEN and SEGO recommend 250 mcg of iodine per day – typically 150–200 mcg from potassium iodide supplements plus iodised salt. AEMPS approves Yoduk and folate combinations (Yodocefol, Natalben) for this indication. Treatment starts 2–3 months before conception and continues throughout pregnancy and lactation. Maternal iodine deficiency reduces the child's IQ and is the most common preventable cause of mild cognitive impairment worldwide per WHO.

Sources

ICD-10: E01.0 · ICD-11: 5A00.1

Thyroid protection in nuclear accident

First line

Thyroid blockade with stable potassium iodide during a radiation emergency releasing iodine-131. and approve the regimen: 130 mg for adults, 65 mg for children 3–18 years, 32 mg for 1 month – 3 years, 16 mg for neonates. The drug is taken on official Civil Protection advisory in the first hours after the release. AEMPS warns: self-administration of potassium iodide outside a radiation event is unjustified and risky – thyrotoxicosis, hypothyroidism and arrhythmia risk. Iosat / ThyroShield / Iodomarin 130 mg are prescription-only for emergency stockpiling; in Spain the stockpile is held by municipal Civil Protection.

Sources

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

Hashimoto thyroiditis (chronic autoimmune thyroiditis)

Not recommended

Biohacker blogs frame high-dose iodine (12.5 mg Iodoral / Lugol protocol, 50 mg Brownstein) as «Hashimoto treatment» and «thyroid activation». Endocrine Society 2017 and SEEN strongly advise against this: in autoimmune thyroiditis excess iodine accelerates gland destruction and shifts patients into hypothyroidism. NIH ODS 2024 notes that milligram iodine doses (60–300 times the daily requirement) are hazardous. Hashimoto management is levothyroxine titrated to TSH under endocrinology supervision, not iHerb Lugol. If milligram iodine has been prescribed without anti-TPO antibody testing, consider a second opinion.

Sources

ICD-10: E06.3 · ICD-11: 5A03.20

Body detoxification and cleansing

Not recommended

Iodine and Lugol protocols are heavily marketed for «thyroid detox», «fluoride and bromine clearance» and «general detoxification». Evidence-based medicine recognises no such indications. AESAN and classify detox claims as unsubstantiated health claims. NIH ODS 2024: milligram iodine doses in people with normal thyroids cause iodine-induced hypothyroidism and thyrotoxicosis (Jod-Basedow phenomenon). AEMPS issued an official 2014 warning about self-administered high-dose risk. Iodine does no «detox» – healthy liver and kidneys clear the blood on their own. Specific symptoms require TSH, free T4, antibodies and endocrinology assessment.

Sources

How to read tiers A–F

AStrong evidence – first or second line in international guidelines
BRecommended in selected cases
CStudy data contradict each other
DBenefit not proven, no documented harm
FDocumented harm, or risk without benefit

Mechanism of action

Iodine is concentrated in the thyroid via the sodium-iodide symporter (NIS) and incorporated into tyrosine residues of thyroglobulin to form thyroxine (T4) and triiodothyronine (T3). Potassium iodide is the pharmaceutical standard with predictable bioavailability. Kelp (Fucus vesiculosus) capsules on iHerb contain iodine with wide variability: from 50 mcg to 3000 mcg per capsule of the same brand – manufacturers often do not control batches. High bolus doses of iodide transiently suppress hormone synthesis (Wolff-Chaikoff effect) – the basis for thyroid blockade after radioactive iodine release.

Safety

Contraindications

Hypersensitivity to iodine or iodides
Dermatitis herpetiformis (Duhring)
Toxic nodular goitre and thyrotoxicosis (for milligram doses)
Active pulmonary tuberculosis
Haemorrhagic diathesis
Age over 40 years – high doses only on strict indication

Serious adverse effects

Iodine-induced thyrotoxicosis (Jod-Basedow) in patients with nodular goitre
Iodine-induced hypothyroidism in patients with Hashimoto thyroiditis
Severe angioedema and anaphylactic reactions
Thyroid storm at high doses in predisposed patients

Common adverse effects

Metallic taste
Nausea, abdominal discomfort
Acne and urticaria
Rhinitis, conjunctivitis (iodism at high doses)
Sialadenitis

Pregnancy: can you take Iodine (umbrella: potassium iodide, kelp / Fucus vesiculosus)?

AEMPS summary of product characteristics for Yoduk (potassium iodide tablets), section 4.6: iodine requirements increase in pregnancy. Iodine and iodine-containing products are given in pregnancy only on an explicit medical indication, based on a benefit-risk assessment. Because iodine crosses the placenta and the fetus is sensitive to pharmacologically active doses of iodine, iodine doses in the milligram range should not be given.

Breastfeeding: can you take Iodine (umbrella: potassium iodide, kelp / Fucus vesiculosus)?

Compatible at prophylactic doses. Hale L2. Iodine concentrates in breast milk; adequate maternal status is critical for infant neurodevelopment. High doses (above 500 mcg/day) can cause infant hypothyroidism and require monitoring.

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

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Frequently asked

What is Iodine (umbrella: potassium iodide, kelp / Fucus vesiculosus) used for?

Iodine (umbrella: potassium iodide, kelp / Fucus vesiculosus) is evaluated for the following indications with varying evidence strength: Iodine deficiency disorders (evidence tier A), Thyroid protection in nuclear accident (evidence tier A), Pregnancy and iodine (evidence tier A). See the full indication matrix with dosing and citations above on this page.

What are the side effects of Iodine (umbrella: potassium iodide, kelp / Fucus vesiculosus)?

Common side effects of Iodine (umbrella: potassium iodide, kelp / Fucus vesiculosus) (≥ 1 in 100): Metallic taste, Nausea, abdominal discomfort, Acne and urticaria, Rhinitis, conjunctivitis (iodism at high doses), Sialadenitis. See the Safety section for uncommon and serious reactions.

Is Iodine (umbrella: potassium iodide, kelp / Fucus vesiculosus) safe during pregnancy?

Is Iodine (umbrella: potassium iodide, kelp / Fucus vesiculosus) compatible with breastfeeding?

Who should not take Iodine (umbrella: potassium iodide, kelp / Fucus vesiculosus)?

Iodine (umbrella: potassium iodide, kelp / Fucus vesiculosus) is contraindicated in: Hypersensitivity to iodine or iodides; Dermatitis herpetiformis (Duhring); Toxic nodular goitre and thyrotoxicosis (for milligram doses); Active pulmonary tuberculosis; Haemorrhagic diathesis. Full list in the Safety section.

Other drugs in this group

Levothyroxine sodium, Potassium iodide, Thiamazole