Bladderwrack: Overview

Alternative names: Sometimes mistakenly written as Bladder Wrack.

Bladderwrack is a type of perennial brown seaweed that grows on the northern Atlantic and Pacific coasts of the United States and on the northern Atlantic coast and Baltic coast of Europe.  The main stem of bladderwrack, known as the thallus, is used medicinally.  It should not be confused with kelp.

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It has been used for conditions associated with the bladder, although its name is probably derived from the bladder-like vesicles along its fronds.  Bladderwrack has been used historically as a diuretic as well as for cases of cystic irritations and chronic inflammations of the bladder.  Bladderwrack was once thought to help reduce obesity and increase muscle mass.  Recently, this use is being explored once again.  Even though little evidence for its use in obesity exists, more research needs to be done in this area.  Some sources of bladderwrack may be significant sources of iodine.  Bladderwrack is considered "Unapproved" under the German Commission E.

Function; Why it is Recommended

There are three major active constituents in bladderwrack: iodine, alginic acid, and fucoidan.

Fucoidan is a type of dietary fiber in bladderwrack that contains numerous sulfur groups.  According to test tube and animal studies, this appears to give fucoidan several properties, such as lowering LDL cholesterol levels, lowering blood glucose levels, anti-inflammatory activity, possible anticoagulant effects, and antibacterial and anti-HIV activity.  Though it has not been definitively proven, fucoidan is thought to prevent bacteria and viruses from binding to human cells, a necessary step in starting an infection, as opposed to killing the microbes directly.  As at the time of writing, no human clinical trials have been done with fucoidan or bladderwrack to support their use for any of these conditions.

As well as the conditions mentioned below, bladderwrack has traditionally been used for: Diarrhea; gastritis; gastroesophageal reflux disease (GERD); improved wound healing (topical application).  Calcium alginate (the calcium salt of alginic acid) has shown promise as an agent to speed wound healing in animal studies, but has not been demonstrated to be effective in humans.

Bladderwrack's mucilaginous thallus has long been used to soothe irritated and inflamed tissues in the body.  It has also been used to counter obesity, possibly due to its reputation for stimulating the thyroid gland.  Clinical research in this area has failed to confirm that seaweeds like bladderwrack help with weight loss, though more specific research is warranted.

Side-Effects; Counter-Indicators and Warnings

Bladderwrack is generally safe, though there are three potential problems with its consumption: acne, thyroid dysfunction, and heavy-metal contamination.  Bladderwrack and other seaweeds that grow in heavy-metal-contaminated waters may contain high levels of these toxins (particularly arsenic and lead), possibly leading to nerve damage, kidney damage or other problems.  Only bladderwrack known to have been harvested from clean water or labeled to indicate the absence of heavy metals or other contaminants should be consumed.

At the time of writing, there were no well-known drug interactions with bladderwrack.

The safety of using bladderwrack during pregnancy and breast-feeding is unknown.  People who are allergic to iodine may need to avoid bladderwrack.

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Bladderwrack can help with the following:



Alginic acid (a component of bladderwrack) is a type of dietary fiber that can be used to help relieve constipation and diarrhea.  However, human studies have at the time of writing not been done on how effective bladderwrack is for either of these conditions.


Bladderwrack has historically been used as a bulk-forming laxative.

Heartburn / GERD / Acid Reflux

An over-the-counter antacid, Gaviscon®, containing magnesium carbonate and sodium alginate (the sodium salt of alginic acid, an active component of bladderwrack), has been shown to effectively relieve the symptoms of heartburn compared to other antacids in a double-blind study. [Chevrel B. A comparative crossover study on the treatment of heartburn and epigastric pain: Liquid Gaviscon® and a magnesium-aluminum antacid gel. J Int Med Res 1980;8: pp300-3]

However, bladderwrack has at the time of writing not been studied for use in people with heartburn.  Bladderwrack might also help indigestion, though again clinical trials have not been conducted.



People living near oceans or seas have a historically low rate of hypothyroidism that is due, in part, to ingestion of iodine-rich food, such as seafood and seaweeds like bladderwrack.  Either hypothyroidism or goiter due to insufficient intake of iodine may possibly improve with bladderwrack supplementation, though human studies have not confirmed this at the time of writing.



Alginic acid has been shown to inhibit HIV in the test tube. [Béress A, Wassermann O, Bruhn T, et al. A new procedure for the isolation of anti-HIV compounds (polysaccharides and polyphenols) from the marine alga Fucus vesiculosus. J Nat Prod 1993;56: pp478-88.]  However, this effect has not been studied in humans.

Lab Values

LDL/HDL Ratio, High

Alginic acid (a component of bladderwrack) may help lower LDL cholesterol levels, according to animal studies.  At the time of writing, no human trials have studied this effect of bladderwrack.


Iodine Requirement

The amount of iodine in bladderwrack is highly variable, probably as a result of different amounts of iodine in the water where it grows.  A reasonable portion of bladderwrack may contain the U.S. adult recommended dietary allowance (RDA) of iodine (150mcg).


Not recommended for
Adolescent Acne

Iodine in any form – including from bladderwrack and other seaweeds – can cause or aggravate acne in some people.

Adult Acne

Iodine in any form – including from bladderwrack and other seaweeds – can cause or aggravate acne in some people.

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May be useful: may help with
May be useful:
may help with
Often counterindicated: is often not recommended for
Often counterindicated:
is often not recommended for
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