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Scientific Name(s): Fucus vesiculosus
Common Name(s): Black tang, Bladder fucus, Brown algae, Brown seaweed, Dyers fucus, Red fucus, Rock wrack, Rockweed

Medically reviewed by Last updated on Jul 24, 2023.

Clinical Overview


Clinical trial data are limited to inform on potential therapeutic applications for F. vesiculosus specifically, with most evidence extrapolated from studies reporting on brown seaweeds generally.


Clinical trials of bladderwrack are lacking to inform dosing recommendations.


Contraindications have not been identified.


Effects on estrogen levels and menstrual cycle length have been reported. Excessive consumption of seaweeds during breastfeeding should probably be avoided due to high iodine content and potential contamination with heavy metals.


None well documented.

Adverse Reactions

GI effects may occur. Transient hypothyroidism due to excess iodine from seaweed has been reported.


Information is limited. Theoretically there is the potential for toxicity due to heavy metal absorption from brown seaweeds; however, case reports are lacking.

Scientific Family


Bladderwrack is a member of the Fucaceae brown algae family. It grows in high-saline content waters at depths of up to 4 m, forming large belts that have an important role in structure of coastal habitats that harbor species-rich epiphytic and epibenthic communities. It is characterized by greenish-brown flattened blades, the ends of which swell during the reproductive season. Airbladders, as floatation devices, have also been described on the fronds.(Catarino 2018) For more information, including regarding related seaweed products, see the Seaweed and Laminaria monographs.


Seaweeds have been used as food and for nutraceutical purposes for centuries. Traditional uses of bladderwrack include the management of inflammatory conditions, diabetes, skin conditions, as well as cancers. Diets rich in seaweed have been associated with longevity (eg, in some Asian countries).(Catarino 2017, Murai 2019, Murray 2018b)


Like most seaweeds, bladderwrack consists of fiber, polysaccharides, minerals (ie, calcium, iodine, magnesium, potassium, sodium, zinc), and vitamins (A, C, and K). Of interest is the alginic acid polysaccharide content (responsible for gel-forming and water-holding properties of Fucus spp.), and the polyphenol phlorotannins.(Catarino 2017, Catarino 2018, Gabbia 2020) The sulphated polysaccharides, also known as fucoidans, are well described and considered responsible for many of the observed anticancer effects of F. vesiculosus.(Senthilkumar 2013) The carotenoid fucoxanthin is also present.(Zaragoza 2008)

Constituents reportedly vary depending on age at harvesting, as well as environmental factors, including the salinity of the water, light exposure, and other seasonal factors.(Catarino 2017)

Uses and Pharmacology

Antimicrobial activity

In vitro data

In vitro studies report antimicrobial activity of Fucus extracts.(Catarino 2017)


Reviews of antiproliferative effects of brown seaweed extracts against human cancer cell lines exist,(Catarino 2017, Moussavou 2014, Zaragoza 2008) with some researchers suggesting activity via immune modulation and interference with cell growth signaling, or via antioxidant activity.(Mathew 2017, Senthilkumar 2013) However, clinical trials are lacking.(Meresse 2020)

Cognitive function/mood

Despite purported activity on cognition and mood, evidence from clinical trials is lacking.(Murray 2018a)

Dermatological effects

Clinical data

Limited studies suggest topical application of a Furcellaria lumbricalis, F. vesiculosus, retinol, conjugated linoleic acid, and glaucine-containing mixture over a 12-week period increases collagen and decreases cellulite in the skin.(Al-Bader 2012) A further clinical study used a F. vesiculosus 1% gel formulation applied over 5 weeks and reported improvement in skin elasticity.(Fujimura 2002)


Animal and in vitro data

A review of the phytochemical properties of brown seaweeds (ie, F. vesiculosus) describes in vitro and animal studies evaluating effects on metabolic syndrome. Brown seaweeds demonstrated potential as food supplements for management of metabolic syndrome.(Gabbia 2020) Activity is largely attributed to inhibition of amylase and glucosidase, thereby decreasing hyperglycemia.(Catarino 2017, Gabbia 2020)

Clinical data

Limited clinical studies have been conducted with F. vesiculosus alone. In a single-dose study evaluating both high-dose (2,000 mg) and low-dose (500 mg) F. vesiculosus extract on postprandial glucose and insulin in volunteers (N=38), no effects versus placebo were observed.(Murray 2018b) Findings of another high-dose, 12-week study by the same researchers are pending.(Murray 2018a)

Clinical studies have reported improved glycemic indices with a brown seaweed capsule preparation containing both Ascophyllum nodosum and F. vesiculosus. A small clinical crossover study (N=23) reported increased plasma insulin levels in response to a carbohydrate test meal. No further studies by the same researchers appear in the literature.(Paradis 2011) In a clinical study evaluating a similar preparation (but with added chromium picolinate) tested over 6 months (N=50), reductions in glycosylated hemoglobin (HbA1C) and blood glucose and insulin levels were observed.(DeMartin 2018) A small clinical trial (N=65) reported improvements in fasting plasma glucose, postprandial plasma glucose, HbA1c, and fasting plasma insulin levels following 6 months of the same preparation.(Derosa 2019) In a 10-week trial of F. vesiculosus extract 1,200 mg/day in 76 overweight and obese adults, improvements in fasting plasma glucose and insulin occurred, but no changes in inflammatory markers or safety markers were observed.(Elidottir 2021)


Animal data

Studies in rodents report that fucoidan-rich brown seaweed extracts reduce serum triglycerides and total and low-density lipoprotein cholesterol levels, and increase high-density lipoprotein cholesterol levels.(Murray 2018a)

Clinical data

Limited clinical studies suggest fucoidan polyphenols may be effective in dyslipidemia.(Murray 2018a)


Inhibitory activity against angiotensin-converting enzyme I (ACEI) has been reported for a Fucus spiralis extract; fucoidans are recognized for their cardiovascular and antihypertensive effects through ACE inhibition.(Catarino 2017, Keleszade 2021) Clinical studies evaluating antihypertensive activity of bladderwrack specifically are lacking. Consumption of seaweed is noted to be associated with a decreased risk for ischemic heart disease.(Murai 2019)


Clinical trials are lacking to inform dosing of bladderwrack.

Pregnancy / Lactation

Information regarding safety and efficacy in pregnancy and lactation is limited. In a small study of premenopausal women with abnormal menstrual cycling histories (N=3), F. vesiculosus consumption increased menstrual cycle length and altered serum and urinary estrogen levels.(Skibola 2004)

Excessive consumption of seaweeds during breastfeeding should probably be avoided due to high iodine content and potential contamination with heavy metals.(NLM 2021) Reports exist of subclinical hypothyroidism related to consumption of large amounts of Undaria pinnatifida seaweed soup by breastfeeding mothers and infants.(Chung 2009, NLM 2021)


Interactions with amiodarone (based on a pharmacokinetic study in rodents),(Rodrigues 2013) ACE inhibitors,(Catarino 2017, Keleszade 2021) medicines dependent on the CYP-450 enzyme system for metabolism,(Mathew 2017) lamotrigine,(Ventura 2020) and vitamin K–influenced anticoagulant agents such as warfarin(Catarino 2018) can theoretically be anticipated; however, case reports are lacking.

Adverse Reactions

Limited clinical studies have been conducted with bladderwrack alone, and case reports are lacking. Minor gastric adverse events have been reported in some seaweed clinical studies, including soft feces and feelings of fullness, possibly due to algin content.(Teas 2009)


Information is limited. Theoretically there is the potential for toxicity due to heavy metal absorption from brown seaweeds; however, case reports are lacking.(Catarino 2018, NLM 2021)

Acute toxicity studies in rodents found no evidence of toxic effects following 4 weeks of daily treatment.(Zaragoza 2008)



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This product may adversely interact with certain health and medical conditions, other prescription and over-the-counter drugs, foods, or other dietary supplements. This product may be unsafe when used before surgery or other medical procedures. It is important to fully inform your doctor about the herbal, vitamins, mineral or any other supplements you are taking before any kind of surgery or medical procedure. With the exception of certain products that are generally recognized as safe in normal quantities, including use of folic acid and prenatal vitamins during pregnancy, this product has not been sufficiently studied to determine whether it is safe to use during pregnancy or nursing or by persons younger than 2 years of age.

Al-Bader T, Byrne A, Gillbro J, et al. Effect of cosmetic ingredients as anticellulite agents: synergistic action of actives with in vitro and in vivo efficacy. J Cosmet Dermatol. 2012;11(1):17-26. doi:10.1111/j.1473-2165.2011.00594.x22360330
Catarino MD, Silva AMS, Cardoso SM. Fucaceae: A source of bioactive phlorotannins. Int J Mol Sci. 2017;18(6):1327. doi:10.3390/ijms1806132728635652
Catarino MD, Silva AMS, Cardoso SM. Phycochemical constituents and biological activities of Fucus spp. Mar Drugs. 2018;16(8):249. doi:10.3390/md1608024930060505
Chung HR, Shin CH, Yang SW, Choi CW, Kim BI. Subclinical hypothyroidism in Korean preterm infants associated with high levels of iodine in breast milk. J Clin Endocrinol Metab. 2009;94(11):4444-4447. doi:10.1210/jc.2009-0632.19808851
De Martin S, Gabbia D, Carrara M, Ferri N. The brown algae Fucus vesiculosus and Ascophyllum nodosum reduce metabolic syndrome risk factors: A clinical study. Nat Prod Commun. 2018;13(12):1691-1694. doi:10.1177/1934578X1801301228
Derosa G, Cicero AFG, D'Angelo A, Maffioli P. Ascophyllum nodosum and Fucus vesiculosus on glycemic status and on endothelial damage markers in dysglicemic patients. Phytother Res. 2019;33(3):791-797. doi:10.1002/ptr.627230714233
Elidottir AS, Sveinsdottir K, Ingadottir B, et al. Seaweed extract improves carbohydrate metabolism in overweight and obese adults. Curr Nutr Food Sci. 2021;17:216-224. doi:10.2174/1573401316999200706012619
Fujimura T, Tsukahara K, Moriwaki S, Kitahara T, Sano T, Takema Y. Treatment of human skin with an extract of Fucus vesiculosus changes its thickness and mechanical properties. J Cosmet Sci. 2002;53(1):1-9.11917251
Gabbia D, De Martin S. Brown seaweeds for the management of metabolic syndrome and associated diseases. Molecules. 2020;25(18):4182. doi:10.3390/molecules2518418232932674
Keleszade E, Patterson M, Trangmar S, Guinan KJ, Costabile A. Clinical efficacy of brown seaweeds Ascophyllum nodosum and Fucus vesiculosus in the prevention or delay progression of the metabolic syndrome: A review of clinical trials. Molecules. 2021;26(3):714. doi:10.3390/molecules2603071433573121
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):572-584. doi:10.1177/153473541668074429096568
Méresse S, Fodil M, Fleury F, Chénais B. Fucoxanthin, a marine-derived carotenoid from brown seaweeds and microalgae: A promising bioactive compound for cancer therapy. Int J Mol Sci. 2020;21(23):9273. doi:10.3390/ijms2123927333291743
Moussavou G, Kwak DH, Obiang-Obonou BW, et al. Anticancer effects of different seaweeds on human colon and breast cancers. Mar Drugs. 2014;12(9):4898-4911. doi:10.3390/md1209489825255129
Murai U, Yamagishi K, Sata M, et al; JPHC Study Group. Seaweed intake and risk of cardiovascular disease: the Japan Public Health Center-based Prospective (JPHC) Study. Am J Clin Nutr. 2019;110(6):1449-1455. doi:10.1093/ajcn/nqz23131518387
Murray M, Dordevic AL, Cox KHM, Scholey A, Ryan L, Bonham MP. Study protocol for a double-blind randomised controlled trial investigating the impact of 12 weeks supplementation with a Fucus vesiculosus extract on cholesterol levels in adults with elevated fasting LDL cholesterol who are overweight or have obesity. BMJ Open. 2018;8(12):e022195. doi:10.1136/bmjopen-2018-02219530552248
Murray M, Dordevic AL, Ryan L, Bonham MP. The impact of a single dose of a polyphenol-rich seaweed extract on postprandial glycaemic control in healthy adults: A randomised cross-over trial. Nutrients. 2018;10(3):270. doi:10.3390/nu1003027029495492
Paradis ME, Couture P, Lamarche B. A randomised crossover placebo-controlled trial investigating the effect of brown seaweed (Ascophyllum nodosum and Fucus vesiculosus) on postchallenge plasma glucose and insulin levels in men and women. Appl Physiol Nutr Metab. 2011;36(6):913-919. doi:10.1139/h11-11522087795
Rodrigues M, Alves G, Abrantes J, Falcão A. Herb-drug interaction of Fucus vesiculosus extract and amiodarone in rats: a potential risk for reduced bioavailability of amiodarone in clinical practice. Food Chem Toxicol. 2013;52:121-128. doi:10.1016/j.fct.2012.11.01223178632
Seaweed. Drugs and Lactation Database (LactMed). National Library of Medicine (US). Updated February 15, 2021. Accessed June 22, 2021.
Senthilkumar K, Manivasagan P, Venkatesan J, Kim SK. Brown seaweed fucoidan: biological activity and apoptosis, growth signaling mechanism in cancer. Int J Biol Macromol. 2013;60:366-374.23817097
Skibola CF. The effect of Fucus vesiculosus, an edible brown seaweed, upon menstrual cycle length and hormonal status in three pre-menopausal women: a case report. BMC Complement Altern Med. 2004;4:10. doi:10.1186/1472-6882-4-1015294021
Teas J, Hurley TG, Hebert JR, Franke AA, Sepkovic DW, Kurzer MS. Dietary seaweed modifies estrogen and phytoestrogen metabolism in healthy postmenopausal women. J Nutr. 2009;139(5):939-944.19321575
Ventura S, Rodrigues M, Falcão A, Alves G. Safety evidence on the administration of Fucus vesiculosus L. (bladderwrack) extract and lamotrigine: data from pharmacokinetic studies in the rat. Drug Chem Toxicol. 2020;43(6):560-566. doi:10.1080/01480545.2018.151845430332899
Zaragozá MC, López D, Sáiz MP, et al. Toxicity and antioxidant activity in vitro and in vivo of two Fucus vesiculosus extracts. J Agric Food Chem. 2008;56(17):7773-7780. doi:10.1021/jf800705318683949

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