Drug & supplement interaction

Fucus Vesiculosus + Hydrochlorothiazide, Metoprolol

Hydrochlorothiazide, Metoprolol brand name: Lopressor HCT.

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

Fucus Vesiculosus has a minor interaction with Hydrochlorothiazide, Metoprolol. Theoretically, concomitant use of Fucus vesiculosus with CYP2D6 substrates might alter the effects of these substrates.

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

Fucus Vesiculosus and Hydrochlorothiazide, Metoprolol

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

Minor

CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES

Why this applies to Hydrochlorothiazide, Metoprolol

Hydrochlorothiazide, Metoprolol falls under CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES — the group Fucus Vesiculosus interacts with.

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.
Severity Minor 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 situation with this combo pill. The metoprolol half is cleared by a liver enzyme called CYP2D6. In lab dishes, a compound in bladderwrack (fucoidan) seemed to both block and speed up that enzyme, so the direction isn't clear, and honestly this has never actually been seen in real people. The hydrochlorothiazide portion doesn't really lean on CYP2D6, so it's not the concern here.

If anything shifted, you might notice more of metoprolol's usual effects (slow pulse, tiredness, dizziness) or less blood pressure control. I wouldn't lose sleep over it, but bladderwrack's bigger issue is its iodine load affecting your thyroid. Loop in your pharmacist or doctor before starting it, especially with heart and blood pressure meds.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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.

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 23 moderate, 867 minor known drug interactions in our database — the Hydrochlorothiazide, Metoprolol one above is one of them. If you take anything else, check it against the full list below.

Moderate 23 Minor 867 No known interaction 1,940 (incl. Hydrochlorothiazide, Metoprolol)
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 Hydrochlorothiazide, Metoprolol

This page covers Fucus Vesiculosus only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Hydrochlorothiazide, Metoprolol page lists 276 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), American Mistletoe (major), Asarabacca (major) and Dolomite (major).

By severity: 11 major · 235 moderate · 30 minor.

From our pharmacist’s overview on the Hydrochlorothiazide, Metoprolol page

“I would treat this list with genuine care. Lopressor HCT combines hydrochlorothiazide, a diuretic, with metoprolol, a beta-blocker, and 276 supplement and herbal ingredients interact with the pair, 11 of them rated major.”

Reviewed by 2 · Jul 18, 2026

Open the Hydrochlorothiazide, Metoprolol interaction page

How much people look this up

Where Fucus Vesiculosus and Hydrochlorothiazide, Metoprolol 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
Top half

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

29 days ago today
Medication Hydrochlorothiazide, Metoprolol
Top 25%

#537 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
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
23Moderate
867Minor
1,939No known interaction
23 Moderate 867 Minor 1,939 No interaction
Moderate

23 interactions

Minor

867 interactions

Showing 60 of 867 minor interactions — see all 867 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 Hydrochlorothiazide, Metoprolol, 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 Hydrochlorothiazide, Metoprolol supplement interactions › Every supplement checked against Hydrochlorothiazide, Metoprolol, 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 Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Fucus Vesiculosus and Hydrochlorothiazide, Metoprolol Together: Common Questions

Can you take Fucus Vesiculosus with Hydrochlorothiazide, Metoprolol?
There is only a minor interaction, which is usually not serious. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Fucus Vesiculosus and Hydrochlorothiazide, Metoprolol interaction?
We rate it Minor. This interaction is generally not clinically significant, but it remains worth noting and discussing with your pharmacist.

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

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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.