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Bladderwrack

natural source of iodine for thyroid support

Evidence · Grade D
Traditional useInteraction riskNeeds more research

Bladderwrack is a brown seaweed rich in iodine, traditionally used for thyroid support, but its high iodine content necessitates cautious use, especially for individuals with thyroid conditions.

Last reviewed June 12, 2026 · AI-assisted, human-reviewed
Bladderwrack (Fucus vesiculosus) is a type of brown seaweed found along the coasts of the Atlantic and Pacific Oceans. It is recognized for its high iodine content, which is essential for thyroid hormone production. Historically, bladderwrack has been used in traditional medicine, particularly for conditions related to thyroid function and metabolism. Its use in modern contexts often centers on its potential role in supporting thyroid health due to this iodine content. Beyond iodine, bladderwrack also contains various other bioactive compounds, including phlorotannins, fucoxanthin, and fucoidans. These compounds are being investigated for potential antioxidant, anti-inflammatory, and immunomodulatory properties. However, the primary focus of its traditional and contemporary use remains its iodine contribution. While bladderwrack is often promoted for thyroid-related concerns, it is crucial to note that excessive iodine intake can be detrimental, especially for individuals with pre-existing thyroid conditions. Therefore, its use requires careful consideration and professional guidance.

Quick answer

What it is: Bladderwrack (Fucus vesiculosus) is a type of brown seaweed found along the coasts of the Atlantic and Pacific Oceans.

May support:Thyroid Nodules, Hypothyroidism, Thyroid Disorders, Subclinical Hypothyroidism

Evidence:Evidence · Grade D

Evidence Summary

Evidence · Grade D

The rationale for bladderwrack's use in thyroid conditions is largely based on its known high iodine content and the established role of iodine in thyroid hormone synthesis. However, direct clinical evidence from controlled human trials specifically evaluating bladderwrack for thyroid nodules, hypothyroidism, or subclinical hypothyroidism is currently lacking. Most claims are extrapolated from the physiological need for iodine.

Last reviewed · Jun 2026

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Why It Works

Bladderwrack provides iodine, a crucial component for the synthesis of thyroid hormones (T3 and T4) by the thyroid gland, thereby potentially supporting normal thyroid function.

How it works in more detail

The primary mechanism of action for bladderwrack is attributed to its high concentration of iodine. Iodine is an essential trace element that the thyroid gland actively uptakes from the bloodstream. Within the thyroid follicular cells, iodine is oxidized and incorporated into tyrosine residues on thyroglobulin, forming monoiodotyrosine (MIT) and diiodotyrosine (DIT). These iodotyrosines are then coupled to form the active thyroid hormones, triiodothyronine (T3) and thyroxine (T4). Adequate iodine supply is critical for maintaining euthyroid status. Beyond iodine, bladderwrack also contains phlorotannins, which are polyphenolic compounds with antioxidant properties, and fucoidans, sulfated polysaccharides that may exhibit anti-inflammatory and immunomodulatory effects, though their direct impact on thyroid function is less established.

How to use

Always consult a qualified clinician.

Editorial guidance

Suggested dosage
No widely accepted consumer dosage due to variable iodine content and safety concerns. Products often suggest dosages ranging from 500 mg to 1500 mg of dried herb or extract, but these are not standardized.
Research dosage range
No established research dosage range for specific thyroid conditions in human trials.
Typical forms
Capsule, Powder, Tincture, Dried herb for tea
Quality markers
Look for products that are third-party tested for iodine content to ensure consistency and to verify the absence of heavy metals and other contaminants. Choose reputable brands that provide certificates of analysis.
Medication interactions
  • Thyroid hormones (e.g., levothyroxine)
  • Antithyroid drugs (e.g., methimazole, propylthiouracil)
  • Lithium (may exacerbate hypothyroidism)
  • Anticoagulants (e.g., warfarin) - theoretical due to fucoidans
Avoid if
  • Hyperthyroidism
  • Autoimmune thyroid disease (e.g., Hashimoto's thyroiditis, Grave's disease)
  • Iodine sensitivity
  • Pregnancy
  • Breastfeeding
  • Thyroid nodules (without medical supervision)
  • Taking thyroid medications

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Suggested dosage

No widely accepted consumer dosage due to variable iodine content and safety concerns. Products often suggest dosages ranging from 500 mg to 1500 mg of dried herb or extract, but these are not standardized.

General guidance — discuss specifics with a clinician.

Active medicinal compounds

Iodine (inorganic and organically bound), Phlorotannins, Fucoidans, Fucoxanthin, Alginic acid.

Traditional use

Bladderwrack has a long history of traditional use, particularly in European folk medicine, where it was employed for goiter (enlarged thyroid gland) due to its iodine content. It was also traditionally used as a remedy for obesity and digestive issues, often as a diuretic and to stimulate metabolism.

Safety

Safety warnings

Due to its high and variable iodine content, bladderwrack can lead to excessive iodine intake, which may induce or exacerbate hyperthyroidism, hypothyroidism, or autoimmune thyroiditis, particularly in susceptible individuals. It may also contain heavy metals or other contaminants depending on its harvesting location. Pregnant or breastfeeding individuals, and those with pre-existing thyroid conditions, should exercise extreme caution and consult a healthcare professional before use.

Avoid if

  • Hyperthyroidism
  • Autoimmune thyroid disease (e.g., Hashimoto's thyroiditis, Grave's disease)
  • Iodine sensitivity
  • Pregnancy
  • Breastfeeding
  • Thyroid nodules (without medical supervision)
  • Taking thyroid medications

Medication interactions

  • Thyroid hormones (e.g., levothyroxine)
  • Antithyroid drugs (e.g., methimazole, propylthiouracil)
  • Lithium (may exacerbate hypothyroidism)
  • Anticoagulants (e.g., warfarin) - theoretical due to fucoidans

Reported side effects

  • Nausea
  • Diarrhea
  • Bloating
  • Thyroid dysfunction (hyperthyroidism or hypothyroidism)
  • Allergic reactions (rare)

General guidance — discuss specifics with a clinician.

Evidence ecosystem

Scientific literature, clinical guidance, government sources, ongoing research, traditional use, and lived experience — grouped by source type and quality.

No indexed evidence yet. We're still building out this remedy's evidence ecosystem.

Limitations: Current evidence is limited by the absence of human clinical trials specifically investigating bladderwrack's efficacy and safety for thyroid disorders. There is a lack of standardized preparations, dosage studies, and long-term safety data. The variability in iodine content in natural bladderwrack products also poses a challenge for consistent therapeutic application and risk assessment.

This page is educational. Statements use phrases like "may support" and "has been studied for"because no remedy here is approved to cure, treat, or reverse any condition. Discussion happens on the ailment pages — community statistics here are derived from those reports. Always consult a qualified clinician.

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