Bladderwrack Introduction

Bladderwrack is also known as Black-tang, Cutweed, Kelpwave, Quercus marina, Seawrack, and Bladder focus. It is seaweed that grows off the Atlantic and Pacific coasts of the US, and is equally abundant off the Atlantic coast of Europe. It can also be found in the North and Baltic seas as well. Bladderwrack’s name is derived from small air bladders that arise from the body of the seaweed, which help to keep it afloat. The total length of the seaweed can be greater than 3 feet. It is a light olive green color when alive and will turn a medium brown when dead and dried. [1]

Much of the information about Bladderwrack is based on its historical usage, and to date, very few research studies have been carried out. Historically, it has been used for conditions of the thyroid, rheumatic conditions, as a laxative, and demulcent. Because of its purported effects upon the thyroid gland, it was also used as an aid for weight loss. [2]

There are three main constituents or ingredients in Bladderwrack.

  • The first is iodine. Iodine found in bladderwrack is responsible for thyroid stimulating activity. The seaweed can have variable amounts of iodine depending on the location it was grown in.
  • The second well-known constituent is alginic acid. This is a fibrous material. Because of the alginic acid component, Bladderwrack is considered as a laxative and lipid-lowering herb.
  • The third constituent is fucoidan. It is a polysaccharide and is the most widely studied constituent of Bladderwrack. Fucoidan is considered an anti-oxidant, anti-inflammatory agent, and may provide for some anti-coagulant activities.

Bladderwrack Uses

Parts used

The whole plant can be used.

Bladderwrack Usage

Currently, the usage of Bladderwrack is not recommended due to highly variable levels of iodine in the plant. Elevated levels of this mineral can have negative effects on thyroid hormone metabolism. [3] However, there are many manufacturers that state the level of iodine contained in a product. These particular supplements may be safely consumed. (see dosage section)

Bladderwrack is also considered unsafe because of the high levels of heavy metal contaminants often found in the plant as a result of water pollution. Again, certain supplements may state that the product is free of any heavy metals. One should always used caution when choosing a Bladderwrack supplement and purchase only those products which come from a reputable manufacturer.

There have not been any studies that document the efficacy of Bladderwrack as a treatment for hypothyroidism. This is based largely on speculation. Anecdotal observations suggest that Bladderwrack can improve symptoms of hypothyroidism, when the condition is caused by a deficiency of iodine.

  • Bladderwrack may be a useful treatment for Type II diabetes mellitus. It has the potential to lower blood sugar. [4] Bladderwrack’s hypoglycemic activity were exhibited in one particular animal study, though the results were statistically insignificant.
  • Bladderwrack has been effective at inhibiting HIV in vitro. [5] The polysaccharide constituents are thought to be primarily responsible for this action. They inhibited reverse transcriptase and were effective when administered in non-toxic doses.
  • Bladderwrack has anti-coagulant activity and may be helpful in conditions of increased blot clot formation, including; thrombophlebitis, DIC, coagulation d/o, and post surgery. [6] Its inhibitory action is caused by Bladderwrack’s chief constituent, fucoidan. Bladderwrack’s action is similar to that of heparin, a mucopolysaccharide produced within the body to prevent the clotting of blood. Heparin is used in the treatment of thrombosis.
  • Bladderwrack has also been shown to lower blood cholesterol. [7] Both alginic acid and fucoidan are thought to be responsible for this activity. Bladderwrack may provide a useful adjunctive therapy for those undergoing standard treatment for high or elevated cholesterol levels.
  • Bladderwrack was found to have anti-estrogenic activity. [8] In a case report of three women, it increased the length of the menstrual cycle, decreased estrogen, and increased the production of progesterone. More studies are needed to determine which conditions Bladderwrack may be most useful for.
  • Bladderwrack is an anti-oxidant. [9] It may be particularly useful for conditions with increased oxidative stress such as cancer, autoimmune diseases, and chronic inflammation.

Bladderwrack Dosages

Bladderwrack is not recommended as a supplement unless the iodine content is stated on the product label and tested for quality control. The recommended dosage of iodine for an adult is 150 mcg (micrograms) per day. Dosages above this amount can cause hyperthyroidism. The over stimulation of the thyroid in conjunction with prolonged high doses of iodine can cause reflex hypothyroidism. [10]

Bladderwrack Toxicities and Contraindications

Toxicity of Bladderwrack is related to increased effects on the production of thyroid hormone. Excess levels of thyroid hormone can cause;

  • increased heart rate
  • palpitations
  • sweating
  • increased weight loss
  • confusion
  • tremor
  • changes to the skin, hair and eyes.

Bladderwrack is contraindicated in pregnancy and lactation due to the high variability of iodine and the possible teratogenic effects (caused by fluctuations in thyroid hormone) it can have on the developing fetus and infant.

It also has the potential to interact with hypoglycemic medications because of its ability to lower the blood sugar. Individuals with diabetes, who are on medications, should regularly check their blood sugar levels and adjust the dosages of such medications accordingly to avoid a hypoglycemic event.

Bladderwrack may also interact with anti-coagulant medications such as heparin and warfarin. Individuals who are on anti-coagulation medications should consult with a physician before beginning treatment with Bladderwrack.

Bladderwrack’s use is also contraindicated for individuals with a bleeding disorder. These individuals are susceptible to an increased hemorrhage, which can cause shock and death from the use of this supplement.


[1] Bladderwrack. January 2005.

[2] Bladderwrack. January 2005.

[3] Bladderwrack. January 2005.

[4] Lamela M, Anca J, Villar R, Otero J, Calleja JM. Hypoglycemic activity of several seaweed extracts. J Ethnopharmacol. 1989 Nov; 27(1-2): 35-43.

[5] Beress A et al. A new procedure for the isolation of anti-HIV compounds (polysaccharides and polyphenols) from the marine algae Fucus vesiculosis. J Nat Prod. 1993 Apr; 56(4): 478-488.

[6] Kuznetsova TA et al. Anticoagulant activity of fucoidan from brown algae Fucus evanesces of the Okhotsk Sea. Bull Exp Biol Med. 2003 Nov; 136(5): 471-473.

[7] Vazquez-Freire MJ et al. Hypolipidemic activity of polysaccharide extract from Fucus vesiculosis. Phytother Res. 1996; 10: 647-650.

[8] Skibola CF. The effect of Fucus vesiculosis, an edible brown seaweed, upon menstrual cycle length, and hormonal status in three pre-menopausal women: a case report. BMC Complement Altern Med. 2004 Aug 4; 4(1): 10.

[9] Ruperez P, Ahrazem O, Leal JA. Potential antioxidant capacity of sulfated polysaccharides from edible marine brown seaweed Fucus vesiculosis. J Agric Food Chem. 2002 Feb 13; 50(4): 840-845.

[10] Bladderwrack. January 2005.


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