Fucus vesiculosus is a type of brown seaweed that grows in the Baltic Sea, Atlantic Ocean, and North Pacific Ocean. The whole plant is used as medicine.

Fucus vesiculosus contains varying amounts of iodine. Iodine might help prevent or treat some thyroid disorders. Fucus vesiculosus also might have antidiabetic effects and affect hormone levels.

People use Fucus vesiculosus for thyroid disorders, obesity, aging skin, constipation, and many other conditions, but there is no good scientific evidence to support these uses.

Don’t confuse Fucus vesiculosus with algin, bladderwort, blue-green algae, ecklonia cava, or laminaria. These are not the same.

There is interest in using Fucus vesiculosus for a number of purposes, but there isn’t enough reliable information to say whether it might be helpful.

When taken by mouth: Fucus vesiculosus is possibly unsafe. It can contain high concentrations of iodine. Taking large amounts of iodine can cause or worsen some thyroid problems. It might also contain heavy metals, which can cause heavy metal poisoning.

When applied to the skin: Fucus vesiculosus is possibly safe.

Special precautions & warnings:

Pregnancy and breast-feeding: Fucus vesiculosus is possibly unsafe to use while pregnant or breast-feeding because it might contain iodine and heavy metals. Don’t use it.

Iodine allergy: Fucus vesiculosus may contain large amounts of iodine, which could cause an allergic reaction in sensitive people. Don’t use it.

Surgery: Fucus vesiculosus might slow blood clotting. It might cause extra bleeding during and after surgery. Stop taking Fucus vesiculosus at least 2 weeks before surgery.

Thyroid disorders: Fucus vesiculosus may contain large amounts of iodine. Long-term use or high doses of iodine might make certain thyroid disorders worse. Also, people with autoimmune thyroid disease might be especially sensitive to the harmful effects of iodine.

Moderate

Be cautious with this combination.

Lithium

Fucus vesiculosus can contain large amounts of iodine. Large amounts of iodine can change thyroid function. Lithium can also change thyroid function. Taking Fucus vesiculosus along with lithium might increase the risk of thyroid function changes.

Medications for an overactive thyroid (Antithyroid drugs)

Fucus vesiculosus can contain large amounts of iodine. Iodine can increase or decrease thyroid function. Taking Fucus vesiculosus along with medications for an overactive thyroid might change the effects of these medications.

Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)

Fucus vesiculosus might slow blood clotting. Taking Fucus vesiculosus along with medications that also slow blood clotting might increase the risk of bruising and bleeding.

Minor

Be watchful with this combination.

Medications changed by the liver (Cytochrome P450 2C8 (CYP2C8) substrates)

Some medications are changed and broken down by the liver. Fucus vesiculosus might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.

Medications changed by the liver (Cytochrome P450 2C9 (CYP2C9) substrates)

Some medications are changed and broken down by the liver. Fucus vesiculosus might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.

Medications changed by the liver (Cytochrome P450 2D6 (CYP2D6) substrates)

Some medications are changed and broken down by the liver. Fucus vesiculosus might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.

Medications changed by the liver (Cytochrome P450 3A4 (CYP3A4) substrates)

Some medications are changed and broken down by the liver. Fucus vesiculosus might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.

Herbs and supplements that might slow blood clotting

Fucus vesiculosus might slow blood clotting and increase the risk of bleeding. Taking it with other supplements with similar effects might increase the risk of bleeding in some people. Examples of supplements with this effect include garlic, ginger, ginkgo, nattokinase, and Panax ginseng.

Strontium

Fucus vesiculosus contains alginate. Alginate can reduce the absorption of strontium. Taking Fucus vesiculosus with strontium supplements might reduce the absorption of strontium.

There are no known interactions with foods.

There isn’t enough reliable information to know what an appropriate dose of Fucus vesiculosus might be. Fucus vesiculosus might also be unsafe because it might contain high amounts of iodine and heavy metals. Speak with a healthcare provider before using.

Black Tang, Bladder Fucus, Bladder Wrack, Bladderwrack, Blasentang, Cutweed, Dyer’s Fucus, Fucus Vésiculeux, Goémon, Kelp, Kelpware, Kelp-Ware, Ocean Kelp, Quercus Marina, Red Fucus, Rockwrack, Sea Kelp, Sea Oak, Seawrack, Varech, Varech Vésiculeux.

To learn more about how this article was written, please see the Natural Medicines Comprehensive Database methodology.

1. Murray M, Dordevic AL, Cox K, Scholey A, Ryan L, Bonham MP. Twelve weeks’ treatment with a polyphenol-rich seaweed extract increased HDL cholesterol with no change in other biomarkers of chronic disease risk in overweight adults: A placebo-controlled randomized trial. J Nutr Biochem 2021;96:108777. View abstract.
2. Heavisides E, Rouger C, Reichel AF, et al. Seasonal Variations in the Metabolome and Bioactivity Profile of Fucus vesiculosus Extracted by an Optimised, Pressurised Liquid Extraction Protocol. Mar Drugs. 2018;16. pii: E503. View abstract.
3. 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;33:791-797. View abstract.
4. 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;16:572-84. View abstract.
5. Wikström SA, Kautsky L. Structure and diversity of invertebrate communities in the presence and absence of canopy-forming Fucus vesiculosus in the Baltic Sea. Estuarine Coastal Shelf Sci 2007;72:168-176.
6. Torn K, Krause-Jensen D, Martin G. Present and past depth distribution of bladderwrack (Fucus vesiculosus) in the Baltic Sea. Aquatic Botany 2006;84:53-62.
7. Hoang TD, Mai VQ, Clyde PW, Shakir MK. Over-the-counter-drug-induced thyroid disorders. Endocr Pract. 2013 Mar-Apr;19:268-74. View abstract.
8. Alraei, RG. Herbal and Dietary Supplements for Weight Loss. Topics in Clinical Nutrition. 2010;25:136-150.
9. Bradley MD, Nelson A Petticrew M Cullum N Sheldon T. Dressing for pressure sores. Cochrane Library 2011;0:0.
10. Schreuder SM, Vermeulen H Qureshi MA Ubbink DT. Dressings and topical agents for donor sites of split-thickness skin grafts. JOURNAL 2009;0:0.
11. Martyn-St James M., O’Meara S. Foam dressings for venous leg ulcers. Cochrane Library. 2012;0:0.
12. Ewart, S Girouard G. Tiller C. et al. Antidiabetic Activities of a Seaweed Extract. Diabetes. 2004;53(Supplement 2):A509.
13. Lindsey, H. Use of Botanicals for Cancer: Systematic Research Required to Determine Role. Oncology Times. 2005;27:52-55.
14. Le Tutour B, Benslimane F, Gouleau MP, and et al. Antioxidant and pro-oxidant activities of the brown algae, Laminaria digitata, Himanthalia elongata, Fucus vesiculosus, Fucus serratus and Ascophyllum nodosum. J Applied Phycology 1998;10:121-129.
15. Eliason, B. C. Transient hyperthyroidism in a patient taking dietary supplements containing kelp. J Am Board Fam.Pract. 1998;11:478-480. View abstract.
16. Gaigi, S., Elati, J., Ben, Osman A., and Beji, C. [Experimental study of the effects of seaweed in the treatment of obesity]. Tunis Med. 1996;74:241-243. View abstract.
17. Drozhzhina, V. A., Fedorov, IuA, Blokhin, V. P., Soboleva, T. I., and Kazakova, O. V. [The use of dental elixirs based on natural biologically active substances in the treatment and prevention of periodontal diseases]. Stomatologiia (Mosk) 1996;Spec No:52-53. View abstract.
18. Yamamoto I, Nagumo T, Fujihara M, and et al. Antitumor effect of seaweeds. II. Fractionation and partial characterization of the polysaccharide with antitumor activity from Sargassum fulvellum. Jpn.J Exp Med 1977;47:133-140. View abstract.
19. Monego, E. T., Peixoto, Mdo R., Jardim, P. C., Sousa, A. L., Braga, V. L., and Moura, M. F. [Different therapies in the treatment of obesity in hypertensive patients]. Arq Bras.Cardiol. 1996;66:343-347. View abstract.
20. Riou D, Colliec-Jouault S, Pinczon du Sel D, and et al. Antitumor and antiproliferative effects of a fucan extracted from ascophyllum nodosum against a non-small-cell bronchopulmonary carcinoma line. Anticancer Res 1996;16(3A):1213-1218. View abstract.
21. Sakata, T. A very-low-calorie conventional Japanese diet: its implications for prevention of obesity. Obes.Res. 1995;3 Suppl 2:233s-239s. View abstract.
22. Ellouali M, Boisson-Vidal C, Durand P, and et al. Antitumor activity of low molecular weight fucans extracted from brown seaweed Ascophyllum nodosum. Anticancer Res 1993;13(6A):2011-2020. View abstract.
23. Drnek, F., Prokes, B., and Rydlo, O. [Experiment in affecting cancer biologically with an intramuscular and local administration of the seaweed, Scenedesmus obliquus]. Cesk.Gynekol. 1981;46:463-465. View abstract.
24. Criado, M. T. and Ferreiros, C. M. Selective interaction of a Fucus vesiculosus lectin-like mucopolysaccharide with several Candida species. Ann Microbiol (Paris) 1983;134A:149-154. View abstract.
25. Shilo, S. and Hirsch, H. J. Iodine-induced hyperthyroidism in a patient with a normal thyroid gland. Postgrad Med J 1986;62:661-662. View abstract.
26. Church FC, Meade JB, Treanor RE, and et al. Antithrombin activity of fucoidan. The interaction of fucoidan with heparin cofactor II, antithrombin III, and thrombin. J Biol Chem 2-25-1989;264:3618-3623. View abstract.
27. Grauffel V, Kloareg B, Mabeau S, and et al. New natural polysaccharides with potent antithrombic activity: fucans from brown algae. Biomaterials 1989;10:363-368. View abstract.
28. Lamela M, Anca J, Villar R, and et al. Hypoglycemic activity of several seaweed extracts. J.Ethnopharmacol. 1989;27(1-2):35-43. View abstract.
29. Maruyama H, Nakajima J, and Yamamoto I. A study on the anticoagulant and fibrinolytic activities of a crude fucoidan from the edible brown seaweed Laminaria religiosa, with special reference to its inhibitory effect on the growth of sarcoma-180 ascites cells subcutaneously implanted into mice. Kitasato Arch Exp Med 1987;60:105-121. View abstract.
30. Obiero, J., Mwethera, P. G., and Wiysonge, C. S. Topical microbicides for prevention of sexually transmitted infections. Cochrane.Database.Syst.Rev. 2012;6:CD007961. View abstract.
31. Park, K. Y., Jang, W. S., Yang, G. W., Rho, Y. H., Kim, B. J., Mun, S. K., Kim, C. W., and Kim, M. N. A pilot study of silver-loaded cellulose fabric with incorporated seaweed for the treatment of atopic dermatitis. Clin.Exp.Dermatol. 2012;37:512-515. View abstract.
32. Michikawa, T., Inoue, M., Shimazu, T., Sawada, N., Iwasaki, M., Sasazuki, S., Yamaji, T., and Tsugane, S. Seaweed consumption and the risk of thyroid cancer in women: the Japan Public Health Center-based Prospective Study. Eur.J.Cancer Prev. 2012;21:254-260. View abstract.
33. Capitanio, B., Sinagra, J. L., Weller, R. B., Brown, C., and Berardesca, E. Randomized controlled study of a cosmetic treatment for mild acne. Clin.Exp.Dermatol. 2012;37:346-349. View abstract.
34. Marais, D., Gawarecki, D., Allan, B., Ahmed, K., Altini, L., Cassim, N., Gopolang, F., Hoffman, M., Ramjee, G., and Williamson, A. L. The effectiveness of Carraguard, a vaginal microbicide, in protecting women against high-risk human papillomavirus infection. Antivir.Ther. 2011;16:1219-1226. View abstract.
35. Cho, H. B., Lee, H. H., Lee, O. H., Choi, H. S., Choi, J. S., and Lee, B. Y. Clinical and microbial evaluation of the effects on gingivitis of a mouth rinse containing an Enteromorpha linza extract. J.Med.Food 2011;14:1670-1676. View abstract.
36. Kang, Y. M., Lee, B. J., Kim, J. I., Nam, B. H., Cha, J. Y., Kim, Y. M., Ahn, C. B., Choi, J. S., Choi, I. S., and Je, J. Y. Antioxidant effects of fermented sea tangle (Laminaria japonica) by Lactobacillus brevis BJ20 in individuals with high level of gamma-GT: A randomized, double-blind, and placebo-controlled clinical study. Food Chem.Toxicol. 2012;50(3-4):1166-1169. View abstract.
37. Arbaizar, B. and Llorca, J. [Fucus vesiculosus induced hyperthyroidism in a patient undergoing concomitant treatment with lithium]. Actas Esp.Psiquiatr. 2011;39:401-403. View abstract.
38. Hall, A. C., Fairclough, A. C., Mahadevan, K., and Paxman, J. R. Ascophyllum nodosum enriched bread reduces subsequent energy intake with no effect on post-prandial glucose and cholesterol in healthy, overweight males. A pilot study. Appetite 2012;58:379-386. View abstract.
39. Paradis, M. E., Couture, P., and 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;36:913-919. View abstract.
40. Misurcova, L., Machu, L., and Orsavova, J. Seaweed minerals as nutraceuticals. Adv.Food Nutr.Res. 2011;64:371-390. View abstract.
41. Jeukendrup, A. E. and Randell, R. Fat burners: nutrition supplements that increase fat metabolism. Obes.Rev. 2011;12:841-851. View abstract.
42. Shin, H. C., Kim, S. H., Park, Y., Lee, B. H., and Hwang, H. J. Effects of 12-week oral supplementation of Ecklonia cava polyphenols on anthropometric and blood lipid parameters in overweight Korean individuals: a double-blind randomized clinical trial. Phytother.Res. 2012;26:363-368. View abstract.
43. Pangestuti, R. and Kim, S. K. Neuroprotective effects of marine algae. Mar.Drugs 2011;9:803-818. View abstract.
44. Miyashita, K., Nishikawa, S., Beppu, F., Tsukui, T., Abe, M., and Hosokawa, M. The allenic carotenoid fucoxanthin, a novel marine nutraceutical from brown seaweeds. J.Sci.Food Agric. 2011;91:1166-1174. View abstract.
45. Araya, N., Takahashi, K., Sato, T., Nakamura, T., Sawa, C., Hasegawa, D., Ando, H., Aratani, S., Yagishita, N., Fujii, R., Oka, H., Nishioka, K., Nakajima, T., Mori, N., and Yamano, Y. Fucoidan therapy decreases the proviral load in patients with human T-lymphotropic virus type-1-associated neurological disease. Antivir.Ther. 2011;16:89-98. View abstract.
46. Oh, J. K., Shin, Y. O., Yoon, J. H., Kim, S. H., Shin, H. C., and Hwang, H. J. Effect of supplementation with Ecklonia cava polyphenol on endurance performance of college students. Int.J.Sport Nutr.Exerc.Metab 2010;20:72-79. View abstract.
47. Odunsi, S. T., Vazquez-Roque, M. I., Camilleri, M., Papathanasopoulos, A., Clark, M. M., Wodrich, L., Lempke, M., McKinzie, S., Ryks, M., Burton, D., and Zinsmeister, A. R. Effect of alginate on satiation, appetite, gastric function, and selected gut satiety hormones in overweight and obesity. Obesity.(Silver.Spring) 2010;18:1579-1584. View abstract.
48. Teas, J., Baldeon, M. E., Chiriboga, D. E., Davis, J. R., Sarries, A. J., and Braverman, L. E. Could dietary seaweed reverse the metabolic syndrome? Asia Pac.J.Clin.Nutr. 2009;18:145-154. View abstract.
49. Irhimeh, M. R., Fitton, J. H., and Lowenthal, R. M. Pilot clinical study to evaluate the anticoagulant a