Herb & supplement monograph

Fucus Vesiculosus Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Fucus Vesiculosus interacts with medications. The heart of this page is the interaction list — every drug Fucus Vesiculosus is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Fucus Vesiculosus is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Fucus Vesiculosus Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, the overall risk of a clinically significant Fucus Vesiculosus drug interaction appears low for most people. None of its known interactions are rated major, and the vast majority are minor and theoretical.

Interactions deserving the most attention

The main concern is bladderwrack's naturally high iodine content, which can affect the thyroid. It deserves the most caution with amiodarone, a heart rhythm drug that is itself rich in iodine, since combining the two could push iodine too high and disturb thyroid function. There is also a reported case of hyperthyroidism in someone taking it with lithium, and it could change how well thyroid hormone or antithyroid medicines work. Anyone on these treatments should have thyroid levels watched closely.

What the rest of the list means

The long list of minor interactions mostly reflects lab studies suggesting a seaweed compound called fucoidan may affect enzymes the body uses to clear many medications, but none of these effects have been reported in people. Similarly, a predicted bleeding risk with blood thinners has not shown up in human research, likely because the compound is poorly absorbed when taken by mouth.

Check your medications against Fucus Vesiculosus

Based on HelloPharmacist’s Fucus Vesiculosus interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Fucus Vesiculosus

893 medications have a known interaction with Fucus Vesiculosus, graded by severity. Select any drug for the full evidence-based detail.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Fucus Vesiculosus using our pharmacist-reviewed interaction data.

AI summaries are generated from our Fucus Vesiculosus interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction 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.
Possible. 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
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Fucus Vesiculosus combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Fucus Vesiculosus affects

Every type of medication (drug category) Fucus Vesiculosus is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 9 drug categories Fucus Vesiculosus interacts with

Amiodarone (cordarone)Antithyroid DrugsLithiumThyroid HormoneAnticoagulant/antiplatelet DrugsCytochrome P450 2c8 (cyp2c8) SubstratesCytochrome P450 2c9 (cyp2c9) SubstratesCytochrome P450 2d6 (cyp2d6) SubstratesCytochrome P450 3a4 (cyp3a4) Substrates

Amiodarone (Cordarone)

Theoretically, combining Fucus vesiculosus with amiodarone might cause excessively high iodine levels.
Fucus vesiculosus contains high concentrations of iodine. Amiodarone contains 37.3% iodine and can increase iodine levels. Concomitant use might increase the risk of having excessive iodine levels and adversely affecting thyroid function. Monitor thyroid function.

Likelihood Probable Evidence D

Antithyroid Drugs

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.

Likelihood Possible Evidence D

Lithium

Concomitant use of Fucus vesiculosus and lithium has resulted in hyperthyroidism.
There is a case of hyperthyroidism occurring in a patient taking Fucus vesiculosus and lithium. Monitor thyroid hormones closely in patients taking lithium and Fucus vesiculosus concomitantly.

Likelihood Possible Evidence D

Thyroid Hormone

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.

Likelihood Possible Evidence D

Anticoagulant/Antiplatelet Drugs

Theoretically, taking Fucus vesiculosus with antiplatelet or anticoagulant drugs might increase the risk of bruising and bleeding.
In vitro evidence suggests that a constituent of Fucus vesiculosus, known as fucoidan, has anticoagulant effects. However, in clinical research, fucoidan does not seem to have significant anticoagulant activity when taken orally, possibly due to poor absorption.

Likelihood Unlikely Evidence D

Cytochrome P450 2C8 (Cyp2C8) Substrates

Theoretically, concomitant use of Fucus vesiculosus with CYP2C8 substrates might increase the risk for adverse effects.
In vitro research shows that fucoidan, a constituent of Fucus vesiculosus, inhibits CYP2C8. This interaction has not been reported in humans.

Likelihood Possible Evidence D

Cytochrome P450 2C9 (Cyp2C9) Substrates

Theoretically, concomitant use of Fucus vesiculosus with CYP2C9 substrates might increase the risk for adverse effects.
In vitro research shows that fucoidan, a constituent of Fucus vesiculosus, inhibits CYP2C9. This interaction has not been reported in humans.

Likelihood Possible Evidence D

Cytochrome P450 2D6 (Cyp2D6) Substrates

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.

Likelihood Possible Evidence D

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.

Likelihood Possible Evidence D

Monograph

Fucus Vesiculosus: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

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.

Scientific name: Fucus vesiculosus
Family: Fucaceae
Part used: Whole plant (thallus/dried seaweed)
Common forms: Capsules, tablets, powder, tea, liquid extract, topical creams and gels

People commonly use it for

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

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallUse caution

Variable, high iodine content can disrupt the thyroid and the plant may concentrate heavy metals.

PregnancyPossibly Unsafe

When used orally because it may contain iodine and heavy metals; avoid using.

Read the full pregnancy detail

BreastfeedingPossibly Unsafe

When used orally because it may contain iodine and heavy metals; avoid using.

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

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Overview

Fucus vesiculosus, most often called bladderwrack, is a type of brown seaweed that grows along the rocky coastlines of the Atlantic and Pacific oceans, including the North Sea and Baltic Sea. It gets the name "bladderwrack" from the small gas-filled bladders that help it float in the water.

People have used bladderwrack for hundreds of years in traditional medicine. Because it naturally contains a lot of iodine, it was historically used to support the thyroid gland. Today it is sold as a dietary supplement in capsules, powders, and teas, and it is also added to some skin creams and gels.

It is often grouped together with "kelp" products, even though bladderwrack and kelp are different seaweeds. This can make labels confusing, so it helps to read product ingredients carefully.

How it works

Bladderwrack contains several compounds that researchers have studied, mostly in the lab. Its main active ingredient is iodine, which the body uses to make thyroid hormones. This is why it can affect thyroid function in both helpful and harmful ways.

It also contains fucoidan and alginates, which are types of complex sugars (polysaccharides) found in brown seaweed. In test-tube and animal studies, these have shown possible anti-inflammatory, antioxidant, and gel-forming effects. The alginates may also act like soluble fiber in the gut.

It is important to know that most of these proposed mechanisms come from laboratory or animal research. Showing an effect in a test tube does not mean the same thing happens in the human body at the amounts found in supplements.

Effectiveness

Does Fucus Vesiculosus work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 12 uses evaluated

12 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

For Fucus Vesiculosus, current evidence isn’t strong enough to rate any specific use. The conditions it has been studied for are listed below.

Also studied for 12 conditions — evidence insufficient to rate

Insufficient Reliable Evidence To Rate Aging skin