Drug & supplement interaction

Fucus Vesiculosus + Testosterone Undecanoate

Testosterone Undecanoate brand names: Andriol, Aveed, Jatenzo, Kyzatrex.

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

Testosterone Undecanoate falls into 2 drug categories that Fucus Vesiculosus can interact with; the most serious is rated moderate. Due to its iodine content, Fucus vesiculosus might alter the effects of thyroid hormone.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions2
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Fucus Vesiculosus and Testosterone Undecanoate

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

Fucus Vesiculosus interacts with whole categories of medication. Testosterone Undecanoate falls into 2 of those categories, so it can interact with Fucus Vesiculosus in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

THYROID HORMONE

1 of 2

Why this applies to Testosterone Undecanoate

Testosterone Undecanoate falls under THYROID HORMONE — the group Fucus Vesiculosus interacts with.

Due to its iodine content, Fucus vesiculosus might alter the effects of thyroid hormone.
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 thyroid hormone could alter the effects of thyroid hormone.
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 something worth clearing up. The interaction on file is really about thyroid hormone medicines, since bladderwrack's iodine can nudge the thyroid in either direction. Testosterone undecanoate is a male hormone (an androgen) used for low testosterone, and it works through a completely different pathway. It isn't a thyroid drug, so the iodine in this seaweed shouldn't directly change how your testosterone works or cause testosterone-type side effects like acne, mood changes, or blood count shifts.

That said, this interaction was matched at the category level, so I'd treat it as a mismatch rather than a real concern for your testosterone. The bigger issue is bladderwrack's iodine affecting your thyroid on its own. If you're considering it, please run it by your pharmacist or doctor first, especially if you have any thyroid history.

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

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

2 of 2

Testosterone Undecanoate also falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES.

Theoretically, concomitant use of Fucus vesiculosus with CYP3A4 substrates might increase the risk for adverse effects.
In vitro research shows that fucoidan, a constituent of Fucus vesiculosus, inhibits CYP3A4. 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 gist: your body uses an enzyme called CYP3A4 to help clear testosterone undecanoate. In lab dishes, a compound in bladderwrack (fucoidan) seems to slow that enzyme down a bit. If that happened in real life, your testosterone could clear a little slower and build up, which in theory could nudge up side effects like acne, oily skin, mood swings, fluid retention, or a higher red blood cell count.

The important part: this is only seen in test tubes, not in actual people. The interaction is rated minor, and bladderwrack's bigger concern is usually its heavy iodine load on the thyroid. Still, before pairing the two, check with your pharmacist or doctor so they can keep an eye on your levels.

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 22 moderate, 868 minor known drug interactions in our database — the Testosterone Undecanoate one above is among them. If you take anything else, check it against the full list below.

Moderate 22 Minor 868 No known interaction 1,940 (incl. Testosterone Undecanoate)
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.

From our Q&A

Questions About Fucus Vesiculosus or Testosterone Undecanoate

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Fucus Vesiculosus or Testosterone Undecanoate, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Testosterone Undecanoate

This page covers Fucus Vesiculosus only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Testosterone Undecanoate page lists 200 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Beer (major), Grapefruit (major), Siberian Cocklebur (major) and St. John's Wort (major).

By severity: 7 major · 150 moderate · 43 minor.

From our pharmacist’s overview on the Testosterone Undecanoate page

“The supplement list for testosterone undecanoate (Jatenzo, Aveed, Kyzatrex, Andriol) deserves real attention before you combine it with much of anything, and the seven major-rated entries are where I would start. Most of the 200 ingredients on file, 121 of them, can change how the body handles this hormone through the CYP3A4 enzyme; gr…”

Reviewed by 2 · Jul 18, 2026

Open the Testosterone Undecanoate interaction page

How much people look this up

Where Fucus Vesiculosus and Testosterone Undecanoate 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 Testosterone Undecanoate
Top 25%

#402 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 Testosterone Injection

What Is Testosterone Injection Used For?

Brand names: Andriol, Aveed, Jatenzo, Kyzatrex

Testosterone injection is primarily used in men whose bodies do not produce enough testosterone on their own — a condition called hypogonadism. This includes primary hypogonadism (a problem with the testicles themselves, such as from injury, infection, or surgery) and hypogonadotropic hypogonadism (caused by problems in the brain's hormone signaling from the hypothalamus or pituitary gland). It is also used to stimulate puberty in carefully selected adolescent males with clearly delayed puberty who have not responded to other support.

Testosterone Enanthate Injection is also approved for use in women with advanced, inoperable metastatic breast cancer (specifically skeletal metastases) who are one to five years past menopause, or in premenopausal women with hormone-responsive breast cancer who have had their ovaries removed. This use should be directed by an oncologist. Aveed (testosterone undecanoate) is specifically approved for male hypogonadism only.

See full Testosterone Injection 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 Testosterone Undecanoate, 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 Testosterone Undecanoate supplement interactions › Every supplement checked against Testosterone Undecanoate, ranked by severity Testosterone Injection 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 Testosterone Undecanoate Together: Common Questions

Can you take Fucus Vesiculosus with Testosterone Undecanoate?
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.
Why are there 2 interactions listed for Fucus Vesiculosus and Testosterone Undecanoate?
Testosterone Undecanoate belongs to more than one drug category, and Fucus Vesiculosus interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Fucus Vesiculosus and Testosterone Undecanoate 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

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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.