Drug & supplement interaction

Ascophyllum Nodosum + Pembrolizumab

Pembrolizumab brand name: Keytruda.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 27, 2026
The bottom line No known interaction

We found no known interaction between Ascophyllum Nodosum and Pembrolizumab in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first.

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Interaction report

Ascophyllum Nodosum and Pembrolizumab

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Pembrolizumab and Ascophyllum Nodosum in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Ascophyllum Nodosum safety at a glance

Ascophyllum Nodosu... overall Use caution Generally used in foods, but its iodine content and possible heavy metal contamination warrant caution.
Pregnancy Avoid Avoid due to high iodine levels and possible contaminants that may affect the baby.
Breastfeeding Avoid Avoid because iodine and contaminants can pass into breast milk.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Pembrolizumab and Ascophyllum Nodosum? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Pembrolizumab

Interactions in our licensed database are recorded against drug classes, not just single drug names. Pembrolizumab is filed under a single classification — antineoplastics. Ascophyllum Nodosum has documented interactions with 3 drug classes — the most serious being amiodarone (cordarone) (moderate), antithyroid drugs (moderate) and thyroid hormone (moderate) — and none of Pembrolizumab’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Ascophyllum Nodosum Does Interact With Other Medications

Ascophyllum Nodosum has 22 moderate known drug interactions in our database — Pembrolizumab isn’t one of them. If you take anything else, check it against the full list below.

Moderate 22 No known interaction 2,808 (incl. Pembrolizumab)
Taking anything else?

Check Another of Your Medications Against Ascophyllum Nodosum

Covers the 2,830 medications we’ve checked against Ascophyllum Nodosum. Pick one to open its full report.

What to actually watch for

What Pembrolizumab’s Own FDA Label Lists

This is not an interaction — none of it involves Ascophyllum Nodosum. These are the most notable effects listed in the ADVERSE REACTIONS section of Pembrolizumab’s own FDA label, for the medication by itself. Knowing the drug’s own list makes it easier to work out the likely cause if something new turns up while you take both. 10 of them are worth acting on rather than waiting out — marked below.

  • Low magnesium Worth acting on
  • A change in thyroid levels Worth acting on
  • Trouble swallowing Worth acting on
  • High potassium Worth acting on
  • Low sodium Worth acting on
  • Low potassium Worth acting on
  • A heart attack Worth acting on
  • Blood clots Worth acting on
  • Heart failure Worth acting on
  • High blood sugar Worth acting on

Showing the 10 most notable of 57 label-listed effects — ranked by how unusual each one is across medicines generally, with serious effects weighted up.

From the ADVERSE REACTIONS section of the FDA label for Pembrolizumab. Read the label on DailyMed › Ascophyllum Nodosum’s licensed record lists no adverse effects our clinical vocabulary could match, so there is no Ascophyllum Nodosum side to compare — that is a limit of the record, not a statement that Ascophyllum Nodosum has no side effects.

Everything else you take

See Every Supplement That Interacts With Pembrolizumab

This page covers Ascophyllum Nodosum only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Pembrolizumab page lists 1 supplement it has a documented interaction with, worst first, each one explained.

The most serious there right now: American Pawpaw (minor).

By severity: 1 minor.

From our pharmacist’s overview on the Pembrolizumab page

“For a drug used against so many different cancers, pembrolizumab (Keytruda) has a remarkably short supplement file. Just one ingredient appears on it, American pawpaw, and even that lone entry is rated minor and judged unlikely to cause real trouble.”

Reviewed by 2 · Jul 18, 2026

Open the Pembrolizumab interaction page

One more smart check

Taking Ascophyllum Nodosum as Part of a Dietary Supplement Product? Check It for Interactions

We hold 360 real supplement products containing Ascophyllum Nodosum, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Ascophyllum Nodosum. Even though Ascophyllum Nodosum itself has no known interaction with Pembrolizumab, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Ascophyllum Nodosum and Pembrolizumab Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Ascophyllum Nodosum
Top 25%

#298 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Pembrolizumab
Top half

#1,054 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Ascophyllum Nodosum reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 27, 2026. The Ascophyllum Nodosum and Pembrolizumab records this page draws on were last updated July 10, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Supplement

About Ascophyllum Nodosum

What is Ascophyllum Nodosum?

Ascophyllum Nodosum
  • Weight management
  • Blood sugar support
  • Thyroid support (iodine source)
  • Digestive health
  • Source of vitamins and minerals
  • Joint comfort

Ascophyllum nodosum (often sold as bladderwrack or brown seaweed) is a nutrient-rich algae that people use for weight, blood sugar, and thyroid support, but solid human evidence is limited for most of these uses. Because it naturally contains iodine and can absorb heavy metals like arsenic, it should be used cautiously, and pregnant or breastfeeding people should avoid it unless a doctor approves.

Ascophyllum nodosum · Fucaceae · Whole seaweed (thallus/fronds) · Capsules, tablets, powder, extracts, teas, and topical products

An interaction check asks whether these two react with each other — it does not ask whether Ascophyllum Nodosum is a good idea for someone in your situation. Here is what our Ascophyllum Nodosum record says about it on its own.

Ascophyllum Nodosum: dosing

There is no well-established standard dose of Ascophyllum nodosum. Products vary widely in strength and iodine content, which makes consistent dosing difficult.If you choose to use it, follow the directions on the product label and do not exceed the recommended amount.

From our Ascophyllum Nodosum monograph — the full record covers uses, side effects and every documented interaction.

Read the full Ascophyllum Nodosum monograph & all interactions
Medication

About Pembrolizumab Injection

What Is Pembrolizumab Injection Used For?

Brand name: Keytruda

Pembrolizumab Injection (Keytruda) is used to treat many types of cancer. Some uses are for cancer that has spread or can’t be removed by surgery. Others are given before or after surgery.

Main cancer types include melanoma, non-small cell lung cancer, mesothelioma, head and neck squamous cell cancer, classical Hodgkin lymphoma, urothelial (bladder) cancer, colorectal cancer, gastric and esophageal cancer, cervical cancer, liver cancer, biliary tract cancer, Merkel cell carcinoma, kidney cancer, endometrial cancer, cutaneous squamous cell carcinoma, triple-negative breast cancer and ovarian cancer. Many uses depend on tumor tests and are given alone or with other cancer drugs.

Most-Reported Side Effects for Pembrolizumab

From FAERS, the FDA’s public side-effect reporting system (0 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Malignant neoplasm progression 12,012 reports
Diarrhea 5,719 reports
Fatigue 5,113 reports
Fever 3,870 reports
Rash 3,719 reports
See full Pembrolizumab Injection drug information
Keep checking

Other Drugs & Ascophyllum Nodosum

Browse every other medication we’ve checked against Ascophyllum Nodosum — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
22Moderate
0Minor
2,807No known interaction
22 Moderate 2,807 No interaction
Moderate

22 interactions

No interaction 2,807 drugs checked — show the list

We also checked Ascophyllum Nodosum against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,807 medications checked with no known interaction — see the full Ascophyllum Nodosum list.

See the full Ascophyllum Nodosum interactions page
See every supplement checked against Pembrolizumab, ranked by severity
Evidence & sources

Ascophyllum Nodosum References

The 5 references that drive our Ascophyllum Nodosum monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  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

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Ascophyllum Nodosum and Pembrolizumab Together: Common Questions

Is it safe to take Ascophyllum Nodosum with Pembrolizumab?
We do not list a known interaction between Ascophyllum Nodosum and Pembrolizumab. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
How was the Ascophyllum Nodosum and Pembrolizumab combination checked?
Interactions in our licensed database are recorded against drug classes. Pembrolizumab is filed under 1 classification, and Ascophyllum Nodosum has documented interactions with 3 drug classes — none of Pembrolizumab's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does Ascophyllum Nodosum interact with any other medications?
Yes. Ascophyllum Nodosum has 22 documented drug interactions in our database — Pembrolizumab is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Pembrolizumab interact with any supplements?
Yes. Pembrolizumab has documented interactions with 1 supplement in our database — Ascophyllum Nodosum is not one of them. The Pembrolizumab interaction page linked on this page lists every one, ranked by severity.

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

Where next

Keep Exploring

Ascophyllum Nodosum monograph Uses, safety profile, and every drug interaction in one place Pembrolizumab Injection drug information The full plain-English guide to this medication Pembrolizumab supplement interactions Every supplement checked against Pembrolizumab, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 5 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Pembrolizumab and Ascophyllum Nodosum?

Our pharmacists answer your medication & supplement questions — free.

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.