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Dietary supplement

Kelp Ingredients & Drug Interactions

by NOW

Kelp label
See full label image
Capsule Category: Other Combinations
Most serious interaction: Moderate
Clinical methodology reviewed by · Updated Sep 23, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking Kelp 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 is a dietary supplement by NOW with 1 active ingredient. Its ingredients are commonly taken for preventing iodine deficiency, supporting thyroid hormone production, general energy and metabolism support.Based on those ingredients, 7 medications have a known interaction with it, the most serious rated moderate. The ingredients most likely to interact are Iodine. 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 by NOW

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

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HelloPharmacist Scorecard of Kelp by NOW

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 Aug 13, 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.

NOW Kelp contains one active ingredient: iodine. Iodine is an essential mineral your body needs for thyroid function and overall metabolism.

The capsule also holds inactive ingredients — cellulose powder, cellulose, and silica — which are fillers and binders that help form and stabilize the capsule.

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: healthy thyroid function.
  • We looked for evidence on: Iodine deficiency, Hyperthyroidism, Thyroid cancer, Thyroid storm, hypothyroidism, goiter.
  • 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 in this product is likely effective for preventing or treating iodine deficiency and for protecting the thyroid after radiation exposure. It's possibly effective for oral mucositis (mouth sores) and periodontitis (gum disease), though the evidence for those uses is less established in our data.

The evidence, ingredient by ingredient Iodine

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.

Iodine from food and normal-dose supplements is well tolerated. High doses, however, can cause thyroid problems — goiter, hypothyroidism (low thyroid function), hyperthyroidism (overactive thyroid), or nodules.

You may also experience abdominal upset, diarrhea, nausea, metallic taste, or headache. Rarely, people have hypersensitivity reactions including rash, swelling, or anaphylaxis.

In pregnancy, adequate iodine matters for your baby's development, but use only the amount your doctor recommends and avoid high-dose products. Some iodine passes into breast milk, so follow your doctor's guidance while breastfeeding.

If you've ever had an iodine hypersensitivity reaction, talk with your doctor or pharmacist before taking this product.

Side effects, ingredient by ingredient Iodine

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 — Iodine.
  • The most serious interaction on file is rated Moderate.
  • Some involve high-stakes drug classes: lithium.
  • For scale: 7 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 your medications before taking this product if you're on lithium, antithyroid drugs (like propylthiouracil or methimazole), or amiodarone — all carry Moderate risk of thyroid function changes or excessive iodine buildup. Your doctor or pharmacist can review your specific prescriptions and decide whether monitoring or a dose adjustment is needed.

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.

NOW Kelp works for iodine deficiency and radiation protection. If you take lithium, antithyroid medication, or amiodarone, check with your doctor or pharmacist first — your thyroid function may need monitoring.

Anyone with a history of iodine sensitivity should also talk it over with their healthcare provider before starting.

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 Apr 25, 2017.

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 NOW
Barcode (UPC) 733739026750
Net contents 250 Veg Capsule(s)
Market status On market
Date entered into DSLD Apr 25, 2017
DSLD ID 73589
Product type Other Combinations
Supplement form Capsule
Dietary claims / uses Nutrient, All Other, Structure/Function
Intended target group(s) Vegan, Vegetarian, Adult (18 - 50 Years), Kosher, Gluten Free, Dairy 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 by NOW, 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 Veg Capsule(s)
Maximum serving Sizes:
1 Veg Capsule(s)
UPC/BARCODE
733739026750
IngredientAmount% DV
Iodine325 mcg217%

Other ingredients: Cellulose powder, Cellulose, Silica

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

Suggested Usage: Take 1 capsule daily with a meal.

Non-GMO

Vegetarian/Vegan

Not manufactured with yeast, wheat, gluten, soy, corn, milk, egg, fish, shellfish or tree nut ingredients.

Brand IP Statement(s)

NOW Kelp delivers the natural nutrient profile found in Genuine Whole Foods.

General Statements

Kelp is a large, leafy seaweed belonging to the brown algae family that grows in "forests" in the colder waters of the world’s oceans. Kelp has been used for centuries as an important nutritious staple ingredient in Chinese, Japanese, and Korean cuisines.

Capsule size

Super green Supports healthy thyroid function*

Botanicals/Herbs Family owned since 1968.

Natural color variation may occur in this product.

Please recycle.

Formula

It is also an excellent source of iodine, which has been shown to be essential for healthy thyroid function.*

325 mcg of natural iodine

Triangle K

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.

Precautions

Caution: For adults only.

Consult physician if pregnant/nursing, taking medication (especially thyroid medications), taking other iodine supplements, or have a medical condition (especially any thyroid disorder).

Keep out of reach of children.

Not manufactured with yeast, wheat, gluten, soy, corn, milk, egg, fish, shellfish or tree nut ingredients. Produced in a GMP facility that processes other ingredients containing these allergens.

General

CODE 2675D V6

Seals/Symbols

Non-GMO

Triangle K

GMP Quality Assured

FDA Statement of Identity

A Dietary Supplement

Storage

Store in a cool, dry place after opening.

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

See for yourself

Kelp by NOW label

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

Kelp 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 by NOW

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

Serving size1 Veg Capsule(s) Dosage formCapsule Amounts shown are per serving.

Iodine

Interacts with
7 drugs
325 mcg per serving Form: organic 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

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

Interaction report

Kelp by NOW 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
7Drugs
7 Moderate

Ingredients driving the most interactions

Iodine 7

Individual Drug Interactions

The ingredients in Kelp interact with 7 drugs. Click any drug to see the details.

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

Each ingredient & the kinds of drugs it affects

For each ingredient in Kelp 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.

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
Iodine full monograph & interactions
The maker

Brand information

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

NOW

See all NOW products
Name
NOW FOODS
Street Address
395 S. Glen Ellyn Rd.
City
Bloomingdale
State
IL
ZipCode
60108
Pharmacist Counseling Corner

Kelp by NOW: Common Questions

Does Kelp by NOW interact with any medications?
Yes. Based on its ingredients, Kelp has a known interaction with 7 medications. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
Kelp 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.
Will this supplement give me enough iodine?
This supplement can help meet or exceed your iodine needs — it's likely effective for preventing or correcting iodine deficiency. The right dose depends on your current intake and health status, so ask your doctor or pharmacist what amount makes sense for you.
Can I take this if I'm pregnant or breastfeeding?
Iodine is important during pregnancy and lactation, but the safety data advises using only the amount your doctor recommends — avoid high-dose products. Some iodine passes into breast milk, so follow medical guidance to protect both you and your baby.
What side effects might I experience?
Most people tolerate iodine well at normal doses. Some experience abdominal upset, diarrhea, nausea, metallic taste, or headache. High doses or prolonged use can cause thyroid problems or acnelike skin lesions. Rarely, hypersensitivity reactions including rash or anaphylaxis occur.
Is this safe if I have a thyroid condition?
Iodine's effect on your thyroid depends on your specific condition — it can raise or lower thyroid function depending on your history. Talk with your doctor or pharmacist before taking this if you have hypothyroidism, hyperthyroidism, thyroid nodules, or any other thyroid issue.
Can this supplement protect my thyroid after radiation?
Yes, iodine is likely effective for protecting thyroid function after radiation exposure. If you've been exposed or are at risk, your doctor or pharmacist can advise you on timing and dosing.

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

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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 label
Go deeper

The Full Monographs Behind Kelp’s Ingredients

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

Herb & supplement monograph

Iodine

Interacts with 7 drugs

Iodine is an essential mineral your body needs to make thyroid hormones, and most people get enough from iodized salt, dairy, and seafood. Supplements help when you are truly deficient, but...

Read the full Iodine monograph →
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 26 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 →

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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