Bladder wrack

Bladder wrack

Bladder wrack

Common Names

  • Sea kelp
  • Brown kelp seaweed
  • Sea wrack
  • Marine oak

For Patients & Caregivers

Claims of beneficial effects of bladder wrack have not been confirmed in clinical studies.

Bladder wrack extract is rich in iodine and is claimed to stimulate thyroid activity to treat obesity. There is no evidence to support this. Women who took bladder wrack showed improvement in their menstrual symptoms. Topical application of a bladder wrack extract showed benefits for skin. Further studies are needed to confirm these effects.

  • Menstrual abnormalities
    In a small study, women who took bladder wrack reported improvement in menstrual symptoms.
  • Skin care
    Results of a clinical trial showed that topical bladder wrack extract can improve the skin.
  • Weight loss
    This use is not supported by scientific evidence.
  • Hypothyroidism
    Bladder wrack is rich in iodine and has been used as a supplement for patients with hypothyroidism caused by iodine deficiency. However, this has not been studied in clinical trials and the dosage used is unclear.
  • Fatigue
    There are no clinical data to support this use.

Patients with thyroid disorder or hormonal-sensitive cancers should talk to their doctors before using bladder wrack.

  • Consumption of a slimming product containing 20 different herbs, bladder wrack being one of them, resulted in hemorrhagic cystitis (inflammation of the urinary bladder) in a 33-year-old woman. Symptoms resolved after discontinuing the product.

Bladder wrack is often referred to as brown kelp but it should not be confused with “kelp,” another species of seaweed.

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For Healthcare Professionals

Maine sea coast vegetables
Fucus vesiculosus

Bladder wrack is a seaweed prevalent on the Atlantic and Pacific coasts from Europe to Asia. It is often referred to as brown kelp but it should not be confused with “kelp,” another species of seaweed. Bladder wrack is consumed as food and medicine and is a rich source of iodine. It is used in traditional medicine to treat hypothyroidism due to iodine deficiency and has been proposed as a weight loss supplement. No clinical studies have verified this effect.
Bladder wrack is believed responsible for the reduced risk of estrogen-related cancers in Asian populations (1) and may improve menstrual symptoms (1). Further studies are needed to clarify such effects.
Bladder wrack extract also demonstrated chemopreventive (7), anti-collagenase and antioxidant properties (6); topical application of bladder wrack extract may help improve skin (2).
Bladder wrack should be used with caution in patients with hormonal-sensitive cancers.

Atlantic sea kelp, seaweed

  • Weight loss
  • Skin care
  • Cellulite
  • Hypothyroidism
  • Fatigue
  • Menstrual abnormalities

Bladder wrack extract is rich in iodine and has been used as a natural supplement for thyroid disorder and for obesity. It has been shown to lower plasma cholesterol levels by competitive inhibition via fucosterols. As cholesterol is a precursor for the biosynthesis of steroid hormones, a reduction in cholesterol bioavailability may lower circulating estradiol levels thereby altering menstrual cycling patterns (1). An extract of bladder wrack reduced 17,beta-estradiol levels and also acted as a competitive inhibitor of estradiol binding to alpha- and beta- estrogen receptors in vitro (3). In rats, treatment with bladder wrack lengthened overall estrous cycles and reduced circulating 17,beta-estradiol levels (4).
Bladder wrack and related seaweed species have been shown to exhibit anti-hypertensive effects via angiotensin-I-converting enzyme inhibition. The antibacterial and antioxidant properties are thought to be due to its polyphenolic contents (1). Topical bladder wrack extract reduced skin thickness and improved the mechanical/elastic properties (2).

Consumption of bladder wrack harvested from polluted waters may cause nephrotoxicity due to the presence of heavy metals such as arsenic, cadmium and mercury (5).

Bladder wrack acts as an estrogenic receptor modulator and should be used with caution in patients with hormonal-sensitive cancers.

  • Consumption of a slimming product containing 20 different herbs, bladder wrack being one of them, resulted in hemorrhagic cystitis in a 33-year-old woman. Symptoms resolved after discontinuing the product (8).
  • Cholesterol-lowering and antihypertensive medications: Theoretically, bladder wrack may have an additive effects (1).
  • Cytochrome P450 substrates: Bladder wrack inhibits cytochrome P450 enzymes, thereby affecting the cellular concentration of drugs that are metabolized by these enzymes (7).
  • Amiodarone: Bladder wrack decreased the bioavailability of amiodarone (used to treat arrythmia) in a study of rats (10).

  1. Fujimura T, Tsukahara K, Moriwaki S, et al. Treatment of human skin with an extract of Fucus vesiculosus changes its thickness and mechanical properties. J Cosmet Sci 2002;53(1):1-9.

  2. Moro CO, Basile G. Obesity and medicinal plants. Fitoterapia 2000;71 Suppl 1:S73-82.

  3. Conz PA, La Greca G, Benedetti P, et al. Fucus vesiculosus: a nephrotoxic alga? Nephrol Dial Transplant 1998;13(2):526-7.

  4. Thring TS, Hili P, Naughton DP. Anti-collagenase, anti-elastase and anti-oxidant activities of extracts from 21 plants. BMC Complement Altern Med. 2009 Aug 4;9:27.

  5. Catania MA, Oteri A, Caiello P, et al. Hemorrhagic cystitis induced by an herbal mixture. South Med J. 2010 Jan;103(1):90-2.

  6. Smith DG, Young EG. On the nitrogenous constituents of Fucus vesiculosus. J Biol Chem. 1953 Dec;205(2):849-58.

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