Bladderwrack (Kelp)
Commonly used for
Metabolic Health
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What is it? / Overview
Bladderwrack and kelp supply iodine, a required substrate for thyroid hormone -- but in iodine-sufficient populations extra iodine doesn't improve thyroid function and can trigger dysfunction, including case-reported hyperthyroidism that resolved after stopping. Kelp can also concentrate heavy metals such as arsenic.
How is it used? / Administration
Form: Bladderwrack (Fucus vesiculosus) or kelp (Laminaria) powder or extract -- iodine content is unpredictable and can be very high
Typical dose studied: No reliable dose -- iodine content varies enormously by product and is often unlabeled
Timing: Not established
Ships deliberately trigger-empty -- there's little upside for most users, and its main value here is so the platform can flag it hard against any reported thyroid condition or thyroid medication if a user reports taking it.
How well does it work? / Evidence
? Emerging / limited evidence
Who should avoid it?
Avoid with: Hypothyroidism / Hashimoto's thyroiditis; Hyperthyroidism / Graves disease; Benign thyroid nodule; Goiter (thyroid enlargement); Breastfeeding
Interacts with: Levothyroxine and antithyroid drugs -- unpredictable iodine load can destabilize dosing; Amiodarone, iodine-containing contrast -- additive iodine load
Already taking it? Given the unpredictable iodine content and case reports of kelp-induced hyperthyroidism, this is worth flagging to a doctor rather than continuing without thyroid monitoring, especially with any preexisting thyroid condition.
Research & references
Farebrother J et al. (2019). Excess Iodine Intake: Sources, Assessment, and Effects on Thyroid Function. Annals of the New York Academy of Sciences. Gherbon A et al. (2019). Transient Hyperthyroidism Following the Ingestion of Complementary Medications Containing Kelp Seaweed: A Case Report. Medicine. Jonklaas J et al. (2014). Guidelines for the Treatment of Hypothyroidism. Thyroid (ATA Task Force).
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