Drug & supplement interaction

Fucus Vesiculosus + Methimazole

Methimazole brand name: Tapazole.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Fucus Vesiculosus has a moderate interaction with Methimazole. Due to its iodine content, Fucus vesiculosus might alter the effects of antithyroid drugs.

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Fucus Vesiculosus and Methimazole

Here is the interaction we found between these two, with the evidence behind it.

Moderate

ANTITHYROID DRUGS

Why this applies to Methimazole

Methimazole falls under ANTITHYROID DRUGS — the group Fucus Vesiculosus interacts with.

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.
Severity Moderate Likelihood Possible Evidence D

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the thing about bladderwrack and methimazole: they're pulling in opposite directions. Methimazole works by telling your overactive thyroid to slow down hormone production. Bladderwrack, on the other hand, is loaded with iodine, and iodine is the raw material your thyroid uses to make hormone. So adding a big iodine load while you're trying to calm the thyroid down can work against your treatment and make your numbers harder to control.

To be fair, this is mostly a theoretical concern based on how iodine behaves, not strong human studies. But since you're managing hyperthyroidism, I'd play it safe. Don't add bladderwrack while on methimazole without checking with your doctor or pharmacist first, since it could throw off your dosing and your thyroid labs.

Contact Dr. Brian directly if you have additional questions on this interaction
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. 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

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Fucus Vesiculosus Also Interacts With Other Medications

Fucus Vesiculosus has 22 moderate, 868 minor known drug interactions in our database — the Methimazole one above is one of them. If you take anything else, check it against the full list below.

Moderate 22 Minor 868 No known interaction 1,940 (incl. Methimazole)
Taking anything else?

Check Another of Your Medications Against Fucus Vesiculosus

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

Everything else you take

See Every Supplement That Interacts With Methimazole

This page covers Fucus Vesiculosus only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Methimazole page lists 64 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Beer (major), Siberian Cocklebur (major), Wine (major) and Ascophyllum Nodosum (moderate).

By severity: 4 major · 51 moderate · 9 minor.

From our pharmacist’s overview on the Methimazole page

“Methimazole (Tapazole) treats an overactive thyroid, and because the drug can stress the liver on its own, this list calls for real vigilance. Of the 64 supplements on file, 4 are rated major, with 51 moderate and 9 minor.”

Reviewed by 2 · Jul 18, 2026

Open the Methimazole interaction page

How much people look this up

Where Fucus Vesiculosus and Methimazole 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 Fucus Vesiculosus
Steady interest

#1,022 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Methimazole
Top half

#1,323 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.

Supplement

About Fucus Vesiculosus

What is Fucus Vesiculosus?

Fucus Vesiculosus
  • Thyroid support
  • Iodine source
  • Weight management
  • Joint and skin care (topical)
  • Constipation and digestive support

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 most of these uses, and its high and variable iodine content can actually harm the thyroid. Talk to a pharmacist or doctor before using it, especially if you have a thyroid condition.

Read the full Fucus Vesiculosus monograph & all interactions
Medication

About Methimazole

What Is Methimazole Used For?

Brand name: Tapazole

Methimazole tablets are used in adults and children with hyperthyroidism (an overactive thyroid) due to Graves' disease or toxic multinodular goiter when surgery or radioactive iodine is not the right option. They work to lower thyroid hormone levels and ease symptoms.

Methimazole tablets are also used to bring thyroid hormone levels down before a patient undergoes thyroidectomy (thyroid surgery) or radioactive iodine treatment, making those procedures safer.

See full Methimazole drug information
Keep checking

Other Drugs & Fucus Vesiculosus

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

0Major
22Moderate
868Minor
1,939No known interaction
22 Moderate 868 Minor 1,939 No interaction
Moderate

22 interactions

Minor

868 interactions

Showing 60 of 868 minor interactions — see all 868 on the Fucus Vesiculosus page.

No interaction 1,939 drugs checked — show the list

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

Showing the 60 most looked-up of 1,939 medications checked with no known interaction — see the full Fucus Vesiculosus list.

See the full Fucus Vesiculosus interactions page
See every supplement checked against Methimazole, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

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

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
Fucus Vesiculosus monograph › Uses, safety, and every drug interaction in one place Methimazole supplement interactions › Every supplement checked against Methimazole, ranked by severity Methimazole drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Fucus Vesiculosus and Methimazole Together: Common Questions

Can you take Fucus Vesiculosus with Methimazole?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Fucus Vesiculosus and Methimazole interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

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

Still Have a Question About Methimazole and Fucus Vesiculosus?

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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.