Interactions on record — worth a quick check against your medications. Check your meds →
Dietary supplement

Kelp Ingredients & Drug Interactions

by Swanson

Tablet Or Pill Category: Other Combinations
Most serious interaction: Moderate
The interaction bottom line Most serious interaction: Moderate

Kelp is a dietary supplement by Swanson with 2 active ingredients. Its ingredients are commonly taken for preventing iodine deficiency, supporting thyroid hormone production, general energy and metabolism support.Based on those ingredients, 23 medications have a known interaction with it, the most serious rated moderate. The ingredients most likely to interact are Atlantic Kelp, Iodine. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

HelloPharmacist Scorecard of Kelp by Swanson

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

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 2 of its 2 active ingredients.
  • No proprietary blends here — you can verify the dose of every single component.

Swanson Kelp contains 2 active ingredients: iodine and Atlantic kelp (Ascophyllum nodosum). Iodine is an essential mineral your body needs to make thyroid hormones and regulate your metabolism.

Atlantic kelp is a brown seaweed that also contains iodine—though your body absorbs its iodine less readily than it does from pure iodine supplements. The tablet also includes several inactive ingredients (fillers and binders): dicalcium phosphate, calcium carbonate, microcrystalline cellulose, stearic acid, silica, magnesium stearate, acacia, and maltodextrin.

Does it work?

Strong evidence
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
Strong

Clinical evidence supports at least one of this product's ingredients for its stated purpose.

Why this rating?
  • The label markets this product for: supports healthy thyroid function and iodine.
  • We looked for evidence on: Iodine deficiency, Hyperthyroidism, Thyroid cancer, Thyroid storm, Hypothyroidism, Thyroid nodules — and 2 related terms.
  • The strongest evidence on file: Iodine is rated "Likely Effective" for Iodine deficiency (Natural Medicines).
  • Also on file: Iodine is rated "Possibly Effective" for Thyroid storm.
  • Also on file: Iodine is rated "Insufficient Reliable Evidence To Rate" for Thyroid cancer, Hyperthyroidism.

Iodine is likely effective for preventing radiation exposure and treating iodine deficiency, and possibly effective for oral mucositis (mouth sores) and periodontitis (gum disease). Atlantic kelp, on the other hand, has insufficient evidence in our data to rate it for prediabetes, obesity, GERD, iodine deficiency, or inflammatory bowel disease.

If you're taking this product for one of Atlantic kelp's intended uses, the science isn't yet established in the information we hold.

The evidence, ingredient by ingredient Iodine Ascophyllum Nodosum

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 2 of the 2 matched ingredients.
  • Pregnancy & breastfeeding safety ratings cover 2 of 2.
  • General safety write-ups exist for 2 of 2.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

Iodine is well tolerated in normal dietary amounts, but high doses can cause thyroid problems—including goiter, hypothyroidism, and hyperthyroidism—and acneform skin lesions (a condition called iododerma) if taken chronically in large quantities. Common side effects at high doses include abdominal upset, diarrhea, headache, metallic taste, nausea, and rhinorrhea.

Rare but serious allergic reactions like anaphylaxis are possible. Atlantic kelp, taken as a supplement, caused elevated thyroid-stimulating hormone (TSH) in 2 out of 22 women in a trial, though free thyroxine (T4) levels remained normal.

For pregnancy and breastfeeding, iodine is rated likely safe in adequate amounts but possibly unsafe in high doses—your doctor should advise the right dose for you. Atlantic kelp should be avoided during pregnancy and breastfeeding because its iodine content and possible heavy metal contaminants can pass to the baby or into breast milk.

Talk with your doctor or pharmacist about whether this product is appropriate for your situation.

Side effects, ingredient by ingredient Iodine Ascophyllum Nodosum

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?
  • 2 of the 2 matched ingredients can interact with medications — Iodine, Ascophyllum Nodosum.
  • The most serious interaction on file is rated Moderate.
  • Some involve high-stakes drug classes: lithium.
  • For scale: 23 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.

Before you take this product, double-check with your doctor or pharmacist if you're on antithyroid medications (moderate risk), lithium (moderate risk), amiodarone (moderate risk), or thyroid hormone replacement (moderate risk). These interactions can alter how your medications work or push your iodine levels too high.

If you take any prescription drug, run it through the checker below.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFully disclosed formula with clinical evidence supporting its stated purpose. Moderate medication interactions have been identified, and safety information is well characterized.

Kelp may help prevent iodine deficiency and protect against radiation exposure, but it's not the right choice if you take antithyroid drugs, lithium, amiodarone, or thyroid hormone replacement. Even if you don't take those medications, high doses of iodine carry real risks to your thyroid.

Before starting, check with your doctor or pharmacist about your specific medications and whether the iodine content is right for you.

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

Assessment coverage: 2 of 2 active ingredients matched to our full ingredient reviews (monographs). Based on the product label dated Jul 24, 2019.

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, straight from the product label.

Brand Swanson
Barcode (UPC) 087614013374
Net contents 250 Tablet(s)
Market status On market
Date entered into DSLD Jul 24, 2019
DSLD ID 203844
Product type Other Combinations
Supplement form Tablet Or Pill
Dietary claims / uses Nutrient, All Other, Structure/Function
Intended target group(s) Adult (18 - 50 Years)
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 by Swanson, 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:
1 Tablet(s)
Maximum serving Sizes:
1 Tablet(s)
UPC/BARCODE
087614013374
IngredientAmount% DV
Iodine225 mcg150%
Atlantic Kelp59 mg--

Other ingredients: Dicalcium Phosphate, Calcium Carbonate, Microcrystalline Cellulose, Stearic Acid, Silica, Magnesium Stearate, Acacia, Maltodextrin

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.
Formula

Great source of Iodine

Iodine source

May contain crustacean shellfish (lobster, crab and shrimp).

General Statements

Supports healthy thyroid function Supports a healthy body weight Science-backed quality since 1969

Thyroid support

Suggested/Recommended/Usage/Directions

Suggested use: As a dietary supplement, take one tablet per day with water. Do not exceed recommended dose.

Precautions

Do not exceed recommended dose.

Warning: For adults only.

Consult your physician before using this or any product if you are pregnant or nursing, taking medication or have a medical condition.

Keep out of reach of children.

Do not use if seal is broken.

May contain crustacean shellfish (lobster, crab and shrimp).

Storage

Store in a cool, dry place.

FDA Disclaimer Statement

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

FDA Statement of Identity

Mineral Supplement

See for yourself

Kelp by Swanson label

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

What’s inside

The Ingredients in Kelp by Swanson

These are the 2 active ingredients this product is made of. Select any to open its full monograph.

Serving size1 Tablet(s) Dosage formTablet Or Pill Amounts shown are per serving.

Most supplement products combine several ingredients, and a medication can interact with the product through any one of them. Each ingredient below shows whether it has known drug interactions.

Iodine

Interacts with
7 drugs
225 mcg per serving Form: Kelp

Iodine is an essential mineral your body needs to make thyroid hormones, and most people get enough from iodized salt, dairy, and seafood. Supplements...

Iodine monograph & interactions

Atlantic Kelp

Interacts with
22 drugs
59 mg per serving Form: Iodine

Ascophyllum nodosum (often sold as bladderwrack or brown seaweed) is a nutrient-rich algae that people use for weight, blood sugar, and thyroid suppor...

Atlantic Kelp monograph & interactions

Other (inactive) ingredients: Dicalcium Phosphate, Calcium Carbonate, Microcrystalline Cellulose, Stearic Acid, Silica, Magnesium Stearate, Acacia, Maltodextrin. These complete the product’s ingredient list but are not active constituents.

Interaction report

Kelp by Swanson Drug Interactions

Want to check YOUR meds against Kelp?

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
23Drugs
23 Moderate

Ingredients driving the most interactions

Iodine 7

Each ingredient & the kinds of drugs it affects

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

Atlantic Kelp3 drug types · 22 drugs

Amiodarone (Cordarone)

Theoretically, combining Ascophyllum nodosum with amiodarone might cause excessively high iodine levels.
Ascophyllum nodosum contains iodine, although the bioavailability of iodine from Ascophyllum nodosum is lower than that of potassium iodide. 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, Ascophyllum nodosum might alter the effects of antithyroid drugs.
Ascophyllum nodosum contains iodine, although the bioavailability of iodine from Ascophyllum nodosum is lower than that of potassium iodide. Iodine in high doses has been reported to cause both hyperthyroidism and hypothyroidism, depending on the individual's past medical history. Taking Ascophyllum nodosum while using antithyroid drugs could alter the effects of the antithyroid drugs.

Likelihood Possible Evidence D
Thyroid Hormone

Due to its iodine content, Ascophyllum nodosum might alter the effects of thyroid hormone.
Ascophyllum nodosum contains iodine, although the bioavailability of iodine from Ascophyllum nodosum is lower than that of potassium iodide. Iodine in high doses has been reported to cause both hyperthyroidism and hypothyroidism, depending on the individual's past medical history. Taking Ascophyllum nodosum while using thyroid hormone could alter the effects of thyroid hormone.

Likelihood Possible Evidence D

Iodine3 drug types · 7 drugs

Amiodarone (Cordarone)

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

Likelihood Probable Evidence D
Antithyroid Drugs

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

Likelihood Probable Evidence D
Lithium

Combining iodine with lithium might have additive hypothyroid effects.
Lithium can inhibit thyroid function. Several case reports suggest that concomitant use of lithium and potassium iodide can reduce thyroid function in otherwise healthy adults. Monitor thyroid function.

Likelihood Probable Evidence D
The maker

Brand information

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

Swanson

See all Swanson products
Name
Swanson Health Products
City
Fargo
State
ND
ZipCode
58104
Phone Number
1-800-437-4148
Web Address
swanson.com
Pharmacist Counseling Corner

Kelp by Swanson: Common Questions

Does Kelp by Swanson interact with any medications?
Yes. Based on its ingredients, Kelp has a known interaction with 23 medications. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
Kelp contains 2 active ingredients, and an interaction can come from any of them. We check every ingredient, combine the results into one list per medication, and show which ingredient and mechanism is 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.
Will this help my iodine deficiency?
Yes—iodine, the main active ingredient in this product, is likely effective for treating iodine deficiency. Atlantic kelp also contains iodine, though your body doesn't absorb it as well. If you suspect you're deficient, talk with your doctor about the right dose for you.
Is it safe to take if I'm pregnant?
Adequate iodine is important in pregnancy, but the facts advise against high-dose products like this one without medical guidance. The safety data for this product in pregnancy is mixed—iodine is rated likely safe at appropriate amounts but possibly unsafe at high doses, and Atlantic kelp should be avoided. You need to talk with your doctor about what's right for your pregnancy.
Can I breastfeed while taking this?
The data advises against Atlantic kelp during breastfeeding because excess iodine and possible heavy metal contaminants can pass into your breast milk. Talk with your doctor or pharmacist about whether iodine supplementation is appropriate for you while breastfeeding.
What are the most common side effects?
At normal dietary iodine levels, this product is well tolerated. At higher doses, some people experience abdominal upset, diarrhea, nausea, metallic taste, headache, or increased nasal secretions. Serious allergic reactions are rare but possible.
Does Atlantic kelp actually work for any conditions?
We don't have enough reliable evidence in our data to rate Atlantic kelp for prediabetes, obesity, GERD, iodine deficiency, or inflammatory bowel disease. The only proven benefits in this product come from the iodine.
Why do I need to be careful with thyroid medications?
Both ingredients contain iodine, which can interfere with how thyroid drugs work. High-dose iodine can trigger either an overactive or underactive thyroid, directly opposing what antithyroid drugs and thyroid hormone replacements are meant to do. If you take any thyroid medication, check with your doctor before starting this product.

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

Not sure if Kelp is safe with your meds?

Our pharmacists answer your medication & supplement questions — free.

Ask a pharmacist

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 label
Sources

Sources & How We Checked

Kelp'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 31 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.

Iodine 26 references
  1. McEvoy GK, ed. AHFS Drug Information. Bethesda, MD: American Society of Health-System Pharmacists, 1998.
  2. Goodman GA, Rall TW, Nies AS, Taylor P. The Pharmacological Basis of Therapeutics, 9th ed.
  3. Ghent WR, Eskin BA, Low DA, Hill LP. Iodine replacement in fibrocystic disease of the breast. Can J Surg 1993;36:453-60.
  4. Potassium iodide for nuclear exposure. Pharmacist's Letter/Prescriber's Letter 2001;17(12):171214.
  5. 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.
  6. Cabezas C, Bustamante B, Holgado W, Begue RE. Treatment of cutaneous sporotrichosis with one daily dose of potassium iodide. Pediatr Infect Dis J 1996;15:352-4. PubMed
  7. 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
  8. Yarrington CD, Pearce EN. Dietary iodine in pregnancy and postpartum. Clin Obstet Gynecol 2011;54:459-70. PubMed
  9. Goel, S., Mandhani, A., Srivastava, A., Kapoor, R., Gogoi, S., Kumar, A., and Bhandari, M. Is povidone iodine an alternative to silver nitrate for renal pelvic instillation sclerotherapy in chyluria? BJU.Int 2004;94(7):1082-1085. PubMed
  10. Teng, W., Shan, Z., Teng, X., Guan, H., Li, Y., Teng, D., Jin, Y., Yu, X., Fan, C., Chong, W., Yang, F., Dai, H., Yu, Y., Li, J., Chen, Y., Zhao, D., Shi, X., Hu, F., Mao, J., Gu, X., Yang, R., Tong, Y., Wang, W., Gao, T., and Li, C. Effect of iodine int
  11. Crawford, B. A., Cowell, C. T., Emder, P. J., Learoyd, D. L., Chua, E. L., Sinn, J., and Jack, M. M. Iodine toxicity from soy milk and seaweed ingestion is associated with serious thyroid dysfunction. Med J Aust. 10-4-2010;193(7):413-415. PubMed
  12. Ohkuma, M. Molluscum contagiosum treated with iodine solution and salicylic acid plaster. Int J Dermatol. 1990;29(6):443-445. PubMed
  13. Connelly KJ, Boston BA, Pearce EN, Sesser D, Snyder D, Braverman LE, Pino S, LaFranchi SH. Congenital hypothyroidism caused by excess prenatal maternal iodine ingestion. J Pediatr. 2012 Oct;161(4):760-2. PubMed
  14. Kasahara T, Narumi S, Okasora K, Takaya R, Tamai H, Hasegawa T. Delayed onset congenital hypothyroidism in a patient with DUOX2 mutations and maternal iodine excess. Am J Med Genet A. 2013 Jan;161A(1):214-7.
  15. Murcia M, Rebagliato M, Iñiguez C, Lopez-Espinosa MJ, Estarlich M, Plaza B, Barona-Vilar C, Espada M, Vioque J, Ballester F. Effect of iodine supplementation during pregnancy on infant neurodevelopment at 1 year of age. Am J Epidemiol. 2011 Apr 1;173(7):8 PubMed
  16. Sang Z, Wang PP, Yao Z, Shen J, Halfyard B, Tan L, Zhao N, Wu Y, Gao S, Tan J, Liu J, Chen Z, Zhang W. Exploration of the safe upper level of iodine intake in euthyroid Chinese adults: a randomized double-blind trial. Am J Clin Nutr. 2012 Feb;95(2):367-73 PubMed
  17. Speeckaert MM, Speeckaert R, Wierckx K, Delanghe JR, Kaufman JM. Value and pitfalls in iodine fortification and supplementation in the 21st century. Br J Nutr. 2011 Oct;106(7):964-73. PubMed
  18. Yun SE, Kang Y, Bae EJ, Hwang K, Jang HN, Cho HS, Chang SH, Park DJ. Iodine-induced thyrotoxic hypokalemic paralysis after ingestion of Salicornia herbace. Ren Fail. 2014 Apr;36(3):461-3.
  19. Iodine Hypersensitivity. Pharmacist's Letter/Prescriber's Letter 2011; 27(5):270504.
  20. Hammel JA, Selby JC. Pustular eruption in a patient with cancer treated with complementary and alternative medicine. JAMA Dermatology 2017 October; E1. doi: 10.1001/jamadermatol.2017.3749. [Epub ahead of print] PubMed
  21. Gil GS, Smith BW, Guerra JR, Williams WT. Acute Delirium in a Hypothyroid Patient Precipitated by Iodine Supplements Use. Am J Ther. 2018;25(6):e717-e718. PubMed
  22. Hamby T, Kunnel N, Dallas JS, Wilson DP. Maternal iodine excess: an uncommon cause of acquired neonatal hypothyroidism. J Pediatr Endocrinol Metab. 2018;31(9):1061-1064. PubMed
  23. Censi S, Watutantrige-Fernando S, Groccia G, et al. The Effects of Iodine Supplementation in Pregnancy on Iodine Status, Thyroglobulin Levels and Thyroid Function Parameters: Results from a Randomized Controlled Clinical Trial in a Mild-to-Moderate Iodine
  24. Rovner MS, Wolf BJ, Rubin M, et al. Instillation of 5% Povidone-Iodine Ophthalmic Drops Decreases the Respiratory Rate in Children Undergoing Strabismus Surgery: A Randomized Controlled Trial. J Pediatr Ophthalmol Strabismus. 2019;56(6):378-382. PubMed
  25. Guenezan J, Garcia M, Strasters D, et al. Povidone Iodine Mouthwash, Gargle, and Nasal Spray to Reduce Nasopharyngeal Viral Load in Patients With COVID-19: A Randomized Clinical Trial. JAMA Otolaryngol Head Neck Surg. 2021;147(4):400-401. PubMed
  26. Li F, Wan S, Zhang L, et al. A Meta-Analysis of the Effect of Iodine Excess on the Intellectual Development of Children in Areas with High Iodine Levels in their Drinking Water. Biol Trace Elem Res 2022;200(4):1580-1590. PubMed

See these in context on the Iodine monograph →

Ascophyllum Nodosum 5 references
  1. 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.
  2. 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
  3. Combet E, Ma ZF, Cousins F, et al. Low-level seaweed supplementation improves iodine status in iodine-insufficient women. Br J Nutr 2014;112:753-61. PubMed
  4. Simmons-Boyce JL, Purcell SL, Nelson CM, MacKinnon SL. Dietary Ascophyllum nodosum increases urinary excretion of tricarboxylic acid cycle intermediates in male Sprague-dawley rats. J Nutr 2009;139:1487-94. PubMed
  5. Sorge US, Henriksen M, Bastan A, et al. Short communication: Iodine concentrations in serum, milk, and tears after feeding Ascophyllum nodosum to dairy cows-A pilot study. J Dairy Sci 2016;99:8472-6. PubMed

See these in context on the Ascophyllum Nodosum 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

Keep exploring