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Dietary supplement

Kelp 400 mg Ingredients & Drug Interactions

by Signature Supplements

Kelp 400 mg label
See full label image
Capsule Category: Botanical
Most serious interaction: Moderate
Clinical methodology reviewed by · Updated Sep 16, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking Kelp 400 mg against your medications. The heart of this page is the interaction checker and the full interaction report — how this product’s ingredients may interact with prescription and over-the-counter medicines you may be taking.

Around that, we add a pharmacist’s high-level view of the product as a whole — what’s inside, the evidence for its stated use, how transparent the label is, and what safety data exists — so you can see the full picture in one place. It’s educational information from our licensed clinical databases and the clinical staff at HelloPharmacist — not medical advice — and we don’t sell or endorse products. Our editorial policy

The interaction bottom line Most serious interaction: Moderate

Kelp 400 mg is a dietary supplement by Signature Supplements with 1 active ingredient. Its ingredients are commonly taken for thyroid support, iodine source, weight management.Based on those ingredients, 891 medications have a known interaction with it, the most serious rated moderate. The ingredients most likely to interact are Kelp. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

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Check Your Meds Against Kelp 400 mg by Signature Supplements

Ask about any prescription or over-the-counter medication and we check it for interactions with Kelp 400 mg by Signature Supplements — and tell you which ingredient is responsible.

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HelloPharmacist Scorecard of Kelp 400 mg by Signature Supplements

Our pharmacy team’s full take, with four database checks built into the cards below — a summary of what is known, not a grade of the product itself.

From our pharmacy team — supplement deep dive

Generated from HelloPharmacist’s pharmacist-curated databases and editorial rules · Last generated Jul 11, 2026

What’s inside

Full disclosure
Ingredient Transparency · database check
Full

Every active ingredient lists its own amount on the label.

Why this rating?
  • The label discloses an exact amount for 1 of its 1 active ingredient.
  • No proprietary blends here — you can verify the dose of every single component.

Kelp 400 mg contains one active ingredient: 400 mg of kelp (Fucus vesiculosus), a brown seaweed. The product also contains two inactive ingredients — cellulose and diatomaceous earth — which serve as a capsule filler and flow agent.

Does it work?

Not established
Evidence for Intended Use · database check
By FDA rules, dietary supplements can’t claim to treat, cure, or prevent disease — so labels speak in careful marketing language. We discern each product’s intended use from its name, label claims, and label statements, then grade the clinical evidence for that use. How these ratings are computed
Not established

The graded evidence we hold for these ingredients covers different conditions than the ones this product is marketed for, so there's no established rating for its stated use — see Fucus Vesiculosus's own graded uses on its monograph.

Why this rating?
  • The label markets this product for: Thyroid support.
  • We looked for evidence on: Hypothyroidism, Iodine deficiency, Thyroid function, Metabolic rate.
  • The closest evidence on file: Fucus Vesiculosus is rated "Insufficient Reliable Evidence To Rate" for Hypothyroidism (Natural Medicines).
  • Also on file: Fucus Vesiculosus is rated "Insufficient Reliable Evidence To Rate" for Iodine deficiency.

The evidence we hold doesn't establish that kelp works for any of the conditions listed in our data — aging skin, heart disease, constipation, diarrhea, and indigestion all show insufficient reliable evidence to rate. That doesn't mean it's ineffective; it means the research either isn't robust enough or we don't have it on file.

If you're thinking about kelp for one of these reasons, ask your pharmacist or doctor what the latest research shows.

The evidence, ingredient by ingredient Fucus Vesiculosus

How safe is it?

Well-documented data
Safety Information · database check
Well characterized

Adverse-effect, pregnancy, and general safety data are on file for most of these ingredients.

Why this rating?
  • We hold adverse-effect (side-effect) data for 1 of the 1 matched ingredient.
  • Pregnancy & breastfeeding safety ratings cover 1 of 1.
  • General safety write-ups exist for 1 of 1.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

Kelp taken by mouth may be unsafe due to its iodine content, which can disrupt thyroid function. The most common side effects are goiter (enlarged thyroid), hyperthyroidism, and hypothyroidism.

A rare serious effect is thyroid cancer. Kelp may also concentrate heavy metals from seawater.

Because of excess iodine and possible heavy metal content, kelp is not recommended during pregnancy. It's also best avoided while breastfeeding, since iodine passes into breast milk and may affect your baby's thyroid.

Side effects, ingredient by ingredient Fucus Vesiculosus

Meds to double-check

Moderate interaction found
Known Interaction Concern · database check
Moderate identified

The most serious documented interaction for these ingredients is Moderate. Check your medications for a personalized result.

Why this rating?
  • 1 of the 1 matched ingredient can interact with medications — Fucus Vesiculosus.
  • The most serious interaction on file is rated Moderate.
  • Some involve high-stakes drug classes: anticoagulant / antiplatelet drugs; lithium.
  • For scale: 892 individual medications appear in the full list. A big number alone doesn't make a product dangerous — what matters is whether YOUR medication is on it, so run yours through the interaction checker on this page.

Check with your pharmacist before taking this product if you take lithium (bipolar disorder), antithyroid drugs, thyroid hormone replacements, or amiodarone for heart rhythm. Also mention blood thinners (anticoagulants and antiplatelet drugs) and any drugs your liver metabolizes — especially if you're unsure of the names.

These are the medication types with documented or theoretical interactions.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFully disclosed formula with no established evidence rating for its marketed use. Moderate medication interactions have been identified, and safety information is well characterized.

Kelp may be worth considering if you're interested in its potential for general health — but it's not for anyone on lithium, thyroid medications, heart rhythm drugs, or blood thinners without talking to their pharmacist first. The high iodine content makes it a medication to cross-check before you start.

If you have any thyroid condition or take any prescription drugs, ask us before taking it.

Educational only — not medical advice; always confirm with your pharmacist. Our editorial policy · How we use AI

Assessment coverage: 1 of 1 active ingredient matched to our full ingredient reviews (monographs). Based on the product label dated Aug 22, 2025.

This Scorecard evaluates available label information, ingredient evidence, and known medication-safety considerations. It does not independently verify product identity, purity, potency, contamination, or manufacturing quality. How these ratings are computed

At a glance

General information

Key facts about Kelp 400 mg, straight from the product label.

Brand Signature Supplements
Net contents 100 Capsule(s)
Market status On market
Date entered into DSLD Aug 22, 2025
DSLD ID 338800
Product type Botanical
Supplement form Capsule
Dietary claims / uses All Other, Structure/Function
Intended target group(s) Adult (18 - 50 Years), Women (not pregnant or lactating), Gluten Free, Dairy Free, Sugar Free
From the label
Everything in this section is reproduced from the manufacturer’s own product label — it’s the label speaking, not HelloPharmacist. We show it so you can see exactly what the maker states; we don’t verify or endorse those statements.

Supplement Facts

The label details for Kelp 400 mg by Signature Supplements, sourced from the NIH Dietary Supplement Label Database.

Supplement Facts

Daily Value (DV) Target Group(s):
Adults and children 4 or more years of age
Minimum serving Sizes:
2 Capsule(s)
Maximum serving Sizes:
2 Capsule(s)
Servings per container
50
IngredientAmount% DV
Kelp800 mg--

Other ingredients: Cellulose, Diatomaceous Earth

Tap any ingredient to jump to its full detail below.

Label statements
These statements are the manufacturer’s wording, reproduced from the product label — the label is saying it, not HelloPharmacist. We don’t verify or endorse them.
Formulation

Contains no: Chemical Fillers or Binders, Artificial coloring, artificial flavor, preservatives, yeast, corn, milk or milk derivatives, lactose, salt, sodium, soy, sugar, gluten, starch or wheat.

From a GMP Facility

Thyroid support

FDA Statement of Identity

Dietary Supplements

Suggested/Recommended/Usage/Directions

Directions: For adults, take two (2) capsules daily, more if needed.

Precautions

As a reminder, discuss the supplements and medications you take with your health care providers.

Warning: Not intended for use by pregnant or nursing women. If you are taking any medications, consult your doctor before use.

Keep out of reach of children.

Storage

Store in a dry place and avoid excessive heat

FDA Disclaimer Statement

This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

Is this label outdated? Report a formula or label change and our pharmacy team will review it.

See for yourself

Kelp 400 mg by Signature Supplements label

The label scan from the NIH Dietary Supplement Label Database. Tap to enlarge.

Kelp 400 mg label

Label images are published by the NIH Dietary Supplement Label Database for the version of this product on file. Always read your actual product label.

View the full label (PDF)
What’s inside

The Ingredients in Kelp 400 mg by Signature Supplements

This is the 1 active ingredient this product is made of. Select it to open its full monograph.

Serving size2 Capsule(s) Dosage formCapsule Servings per container50 Amounts shown are per serving.

Kelp

Interacts with
891 drugs
800 mg per serving Form: Fucus vesiculosus

Fucus vesiculosus (bladderwrack) is a brown seaweed rich in iodine that has been used traditionally for thyroid concerns, weight, and skin. There is l...

Kelp monograph & interactions

Other (inactive) ingredients: Cellulose, Diatomaceous Earth. These complete the product’s ingredient list but are not active constituents.

Interaction report

Kelp 400 mg by Signature Supplements Drug Interactions

Want to check YOUR meds against Kelp 400 mg?

Ask about interactions with your drugs in plain English — “Can I take it with lisinopril?” — and we find you the answer in seconds, ingredient by ingredient.

 Go to the checker
891Drugs
23 Moderate 868 Minor

Ingredients driving the most interactions

Kelp 891

Individual Drug Interactions

The ingredients in Kelp 400 mg interact with 891 drugs. Click any drug to see the details.

1 of the 1 ingredient in Kelp 400 mg interact with drugs. Each result below shows which ingredient is responsible. Kelp

Each ingredient & the kinds of drugs it affects

For each ingredient in Kelp 400 mg with known interactions, here are the types of medications it can affect. Open any type for the detail — or search your exact drug in the checker above.

Kelp9 drug types · 891 drugs

Amiodarone (Cordarone)

Theoretically, combining Fucus vesiculosus with amiodarone might cause excessively high iodine levels.
Fucus vesiculosus contains high concentrations of iodine. Amiodarone contains 37.3% iodine and can increase iodine levels. Concomitant use might increase the risk of having excessive iodine levels and adversely affecting thyroid function. Monitor thyroid function.

Likelihood Probable Evidence D
Antithyroid Drugs

Due to its iodine content, Fucus vesiculosus might alter the effects of antithyroid drugs.
Fucus vesiculosus contains high concentrations of iodine. Iodine in high doses has been reported to cause both hyperthyroidism and hypothyroidism, depending on the individual's past medical history. Taking Fucus vesiculosus while using antithyroid drugs could alter the effects of the antithyroid drugs.

Likelihood Possible Evidence D
Lithium

Concomitant use of Fucus vesiculosus and lithium has resulted in hyperthyroidism.
There is a case of hyperthyroidism occurring in a patient taking Fucus vesiculosus and lithium. Monitor thyroid hormones closely in patients taking lithium and Fucus vesiculosus concomitantly.

Likelihood Possible Evidence D
Thyroid Hormone

Due to its iodine content, Fucus vesiculosus might alter the effects of thyroid hormone.
Fucus vesiculosus contains high concentrations of iodine. Iodine in high doses has been reported to cause both hyperthyroidism and hypothyroidism, depending on the individual's past medical history. Taking Fucus vesiculosus while using thyroid hormone could alter the effects of thyroid hormone.

Likelihood Possible Evidence D
Anticoagulant/Antiplatelet Drugs

Theoretically, taking Fucus vesiculosus with antiplatelet or anticoagulant drugs might increase the risk of bruising and bleeding.
In vitro evidence suggests that a constituent of Fucus vesiculosus, known as fucoidan, has anticoagulant effects. However, in clinical research, fucoidan does not seem to have significant anticoagulant activity when taken orally, possibly due to poor absorption.

Likelihood Unlikely Evidence D
Cytochrome P450 2C8 (Cyp2C8) Substrates

Theoretically, concomitant use of Fucus vesiculosus with CYP2C8 substrates might increase the risk for adverse effects.
In vitro research shows that fucoidan, a constituent of Fucus vesiculosus, inhibits CYP2C8. This interaction has not been reported in humans.

Likelihood Possible Evidence D
Cytochrome P450 2C9 (Cyp2C9) Substrates

Theoretically, concomitant use of Fucus vesiculosus with CYP2C9 substrates might increase the risk for adverse effects.
In vitro research shows that fucoidan, a constituent of Fucus vesiculosus, inhibits CYP2C9. This interaction has not been reported in humans.

Likelihood Possible Evidence D
Cytochrome P450 2D6 (Cyp2D6) Substrates

Theoretically, concomitant use of Fucus vesiculosus with CYP2D6 substrates might alter the effects of these substrates.
In vitro research shows that fucoidan, a constituent of Fucus vesiculosus, both inhibits and induces CYP2D6. This interaction has not been reported in humans.

Likelihood Possible Evidence D
Cytochrome P450 3A4 (Cyp3A4) Substrates

Theoretically, concomitant use of Fucus vesiculosus with CYP3A4 substrates might increase the risk for adverse effects.
In vitro research shows that fucoidan, a constituent of Fucus vesiculosus, inhibits CYP3A4. This interaction has not been reported in humans.

Likelihood Possible Evidence D
Kelp full monograph & interactions
The maker

Brand information

Manufacturer and brand details for Kelp 400 mg, from the product label.

Signature Supplements

See all Signature Supplements products
Name
Signature Supplements
Street Address
P.O. Box 1112
City
San Clemente
State
CA
Web Address
yoursignaturesupplements.com
Pharmacist Counseling Corner

Kelp 400 mg by Signature Supplements: Common Questions

Does Kelp 400 mg by Signature Supplements interact with any medications?
Yes. Based on its ingredients, Kelp 400 mg has a known interaction with 891 medications. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
Kelp 400 mg contains a single active ingredient, and that one ingredient can interact with many different medications on its own. We check it against each medication and show the mechanism responsible.
Where does this information come from?
The product label data comes from the NIH Dietary Supplement Label Database (DSLD); the interaction data is built on the Natural Medicines database and reviewed by HelloPharmacist pharmacists.
Is kelp safe to take while I'm pregnant or breastfeeding?
No. The safety data advises against kelp during pregnancy because of excess iodine and possible heavy metal content. If you're breastfeeding, iodine passes into breast milk and may affect your baby's thyroid, so it's best avoided then too. Talk with your doctor or pharmacist about whether kelp is right for you in these stages.
What are the most common side effects of taking kelp by mouth?
The most common side effects are goiter (an enlarged thyroid), hyperthyroidism (overactive thyroid), and hypothyroidism (underactive thyroid) — all related to its high iodine content. A rare serious effect is thyroid cancer.
Does the kelp in this product actually work for skin aging, heart health, or digestion?
We don't have reliable evidence in our data to say whether kelp works for aging skin, heart disease, constipation, diarrhea, or indigestion. The research either isn't strong enough or we don't have it on file. Your pharmacist can tell you what the latest studies show.
Why is the iodine in kelp a problem?
Kelp contains very high amounts of iodine, which can disrupt how your thyroid works. High-dose iodine can cause both an overactive and underactive thyroid depending on your history, and it can interfere with medications used to treat thyroid and heart conditions.
Can kelp concentrate heavy metals?
Yes. Kelp — being a seaweed — can absorb and concentrate heavy metals from seawater. This is noted as a safety concern in the data we hold.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Not sure if Kelp 400 mg is safe with your meds?

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Label information is sourced from the NIH Dietary Supplement Label Database and reflects the product version on file; always read your actual product label. This page is for education only and is not a substitute for professional medical advice. Confirm with your pharmacist or doctor before combining supplements and medications.

Kelp 400 mg label
Go deeper

The Full Monographs Behind Kelp 400 mg’s Ingredients

Every ingredient we hold a full HelloPharmacist monograph for — uses, evidence, safety, and the complete interaction list.

Herb & supplement monograph

Fucus Vesiculosus

Interacts with 891 drugs

Fucus vesiculosus (bladderwrack) is a brown seaweed rich in iodine that has been used traditionally for thyroid concerns, weight, and skin. There is little solid human evidence to support mo...

Read the full Fucus Vesiculosus monograph →
Sources

Sources & How We Checked

Kelp 400 mg's label data comes from the NIH Dietary Supplement Label Database; the ingredient interaction data is from the Natural Medicines database, reviewed by our pharmacists.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

The 15 references behind this product’s interaction data

Every citation that drives the interaction findings for this product’s ingredients, from the evidence-graded Natural Medicines (TRC Healthcare) database. Open an ingredient to browse its citations — links open the study on PubMed or the publisher’s site.

Fucus Vesiculosus 15 references
  1. Goodman GA, Rall TW, Nies AS, Taylor P. The Pharmacological Basis of Therapeutics, 9th ed.
  2. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2002.
  3. Phaneuf D, Cote I, Dumas P, et al. Evaluation of the contamination of marine algae (Seaweed) from the St. Lawrence River and likely to be consumed by humans. Environ Res 1999;80:S175-S182. PubMed
  4. Durig J, Bruhn T, Zurborn KH, et al. Anticoagulant fucoidan fractions from Fucus vesiculosus induce platelet activation in vitro. Thromb Res 1997;85:479-91. PubMed
  5. Conz PA, La Greca G, Benedetti P, et al. Fucus vesiculosus: a nephrotoxic alga? Nephrol Dial Transplant 1998;13:526-7.
  6. Ohye H, Fukata S, Kanoh M, et al. Thyrotoxicosis caused by weight-reducing herbal medicines. Arch Intern Med 2005;165:831-4. PubMed
  7. Okamura K, Inoue K, Omae T. A case of Hashimoto's thyroiditis with thyroid immunological abnormality manifested after habitual ingestion of seaweed. Acta Endocrinol (Copenh) 1978;88:703-12. PubMed
  8. Agarwal SC, Crook JR, Pepper CB. Herbal remedies -- how safe are they? A case report of polymorphic ventricular tachycardia/ventricular fibrillation induced by herbal medication used for obesity. Int J Cardiol 2006;106:260-1. PubMed
  9. Sterling JB, Heymann WR. Potassium iodide in dermatology: a 19th century drug for the 21st century-uses, pharmacology, adverse effects, and contraindications. J Am Acad Dermatol 2000;43:691-7. PubMed
  10. Catania, M. A., Oteri, A., Caiello, P., Russo, A., Salvo, F., Giustini, E. S., Caputi, A. P., and Polimeni, G. Hemorrhagic cystitis induced by an herbal mixture. South.Med.J. 2010;103(1):90-92. PubMed
  11. Cumashi, A., Ushakova, N. A., Preobrazhenskaya, M. E., D'Incecco, A., Piccoli, A., Totani, L., Tinari, N., Morozevich, G. E., Berman, A. E., Bilan, M. I., Usov, A. I., Ustyuzhanina, N. E., Grachev, A. A., Sanderson, C. J., Kelly, M., Rabinovich, G. A., I
  12. Irhimeh, M. R., Fitton, J. H., and Lowenthal, R. M. Pilot clinical study to evaluate the anticoagulant activity of fucoidan. Blood Coagul.Fibrinolysis 2009;20(7):607-610. PubMed
  13. Arbaizar, B. and Llorca, J. [Fucus vesiculosus induced hyperthyroidism in a patient undergoing concomitant treatment with lithium]. Actas Esp.Psiquiatr. 2011;39(6):401-403.
  14. Church FC, Meade JB, Treanor RE, and et al. Antithrombin activity of fucoidan. The interaction of fucoidan with heparin cofactor II, antithrombin III, and thrombin. J Biol Chem 2-25-1989;264(6):3618-3623. DOI
  15. Mathew L, Burney M, Gaikwad A, et al. Preclinical evaluation of safety of fucoidan extracts from Undaria pinnatifida and Fucus vesiculosus for use in cancer treatment. Integr Cancer Ther 2017;16(4):572-84.

See these in context on the Fucus Vesiculosus monograph →

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

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