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See Also in Complementary & Alternative Medicine

Herbal medicine

Hypothyroidism

Kelp

Complementary & Alternative Medicine

Bladderwrack

by EBSCO CAM Review Board

Category: Herbs and supplements

Related terms: Black tang, cut weed, Fucus vesiculosus, rockweed, rockwrack, seawrack

Definition: Natural plant product used to treat specific health conditions.

Principal proposed uses: None

Other proposed uses: Atherosclerosis, constipation, heartburn, hypothyroidism caused by iodine deficiency, immune support

Overview

Bladderwrack is a type of seaweed found on the coasts of the North Sea, the western Baltic Sea, and the Atlantic and Pacific Oceans. A common food in Japan, it is used as an additive and flavoring in various food products in Europe. Bladderwrack is commonly found as a component of kelp tablets or powders used as nutritional supplements. It is sometimes loosely called kelp, but that term technically refers to a different seaweed.

Bladderwrack contains high concentrations of iodine, and for this reason it has been recommended as a treatment for hypothyroidism (underactive thyroid gland). However, iodine will only help for the type of hypothyroidism caused by iodine deficiency, which is a relatively rare condition in the developed world.

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Therapeutic Dosages

It is important not to take bladderwrack in dosages providing more than the recommended daily intake of iodine. Products that provide bladderwrack should state the amount of iodine they provide. Only products stating the amount of iodine should be used.

Therapeutic Uses

Bladderwrack contains high concentrations of iodine, and for this reason it has been recommended as a treatment for hypothyroidism (underactive thyroid gland). However, iodine will help only for the type of hypothyroidism caused by iodine deficiency, which is a relatively rare condition in the developed world. If a person’s iodine levels are not low, taking extra amounts of iodine can cause the thyroid gland to become either over- or underactive, causing hyperthyroidism or hypothyroidism, respectively. Furthermore, the amount of iodine supplied by bladderwrack is unpredictable.

A component of bladderwrack called alginic acid swells upon contact with water. When taken orally, it forms a type of seal at the mouth of the stomach and for this reason is used in over-the-counter preparations for heartburn. The same constituent gives bladderwrack laxative properties as well. Other proposed uses of bladderwrack include treating atherosclerosis and strengthening immunity, but there is no meaningful evidence at present that it works for these purposes.

Safety Issues

Studies have found that levels of iodine vary widely among bladderwrack products. Because of this, if a person uses bladderwrack as a regular supplement, the individual may receive an overdose of iodine and develop hyperthyroidism or hypothyroidism. Bladderwrack and other seaweed preparations can also worsen acne and decrease iron absorption.

Finally, bladderwrack, like other sea plants, can concentrate toxic heavy metals, such as arsenic, from the surrounding sea water. One report suggests that use of a bladderwrack product with a high heavy metal content is responsible for a case of kidney failure. Heavy metals present particular risks for pregnant or nursing women, children, individuals with kidney disease, or anyone using bladderwrack in high doses or over a long period of time.

Further Reading

1 

Conz, P. A., et al. “Fucus vesiculosus: A Nephrotoxic Alga?” Nephrology Dialysis Transplantation 13 (1998): 526-527.

2 

Norman, J. A., et al. “Human Intake of Arsenic and Iodine from Seaweed-Based Food Supplements and Health Foods Available in the UK.” Food Additives and Contaminants 5 (1987): 103-109.

Citation Types

Type
Format
MLA 9th
, EBSCO CAM Review Board. "Bladderwrack." Complementary & Alternative Medicine, edited by Richard P. Capriccioso & Paul Moglia, Salem Press, 2012. Salem Online, online.salempress.com/articleDetails.do?articleName=CAM_0089.
APA 7th
, E. C. (2012). Bladderwrack. In R. P. Capriccioso & P. Moglia (Eds.), Complementary & Alternative Medicine. Salem Press. online.salempress.com.
CMOS 17th
, EBSCO CAM Review Board. "Bladderwrack." Edited by Richard P. Capriccioso & Paul Moglia. Complementary & Alternative Medicine. Hackensack: Salem Press, 2012. Accessed December 14, 2025. online.salempress.com.