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What is Seaweed?

Seaweeds are marine algae, saltwater-dwelling, simple plants, including red, brown, and green algae. Most algae have root-like structures called holdfasts that anchor the plant to rocks and other substrates. While blue-green species are called algae, they are actually bacteria.

Scientific Name(s)

More than 9,000 species exist, including Ascophyllum, Chondrus, Ecklonia, Fucus, Gelidium, Gracilaria, Laminaria, Phaeophycota, Pterocladia, and Rhodophyceae.

Common Name(s)

Seaweed is also known as brown seaweed, red seaweed, algae, kelp, egg wrack, kombu/konbu, sea spaghetti, wakame, nori, dulse/dillisk, sea lettuce, sea grass, carrageenin, and Irish moss.

What is it used for?

Traditional/Ethnobotanical uses

For centuries, seaweed has been of botanical, industrial, and pharmaceutical interest. Because of the high nutrient content, seaweed has been used as a food throughout Asia.

Traditional Chinese medicine used hot water extracts of certain seaweeds in the treatment of cancer. Additionally, the Japanese and Chinese cultures have used seaweeds to treat goiter and other glandular problems since 300 BC.

The Romans used seaweeds in the treatment of wounds, burns, and rashes. The Celts noted that ordinary seaweed contracted as it dried and then expanded with moisture. In Scotland during the 18th century, physicians used dried seaweed stem to successfully drain abdominal wall abscesses. They also inserted seaweed into the cervix in an attempt to treat dysmenorrhea. Many reports outline the use of seaweed to induce abortion. Seaweed was employed intravaginally for ripening of the cervix and was used rectally for strictures.

General uses

There are few clinical trials to support therapeutic recommendations for seaweeds. However, seaweeds are an important source of minerals and are low in sodium. They may be useful in heart conditions due to cholesterol reduction and appetite suppression. Alginates extracted from seaweed have been used in wound dressings.

What is the recommended dosage?

Clinical trials have used an oral dosage range of 4 to 12 g seaweed daily for up to 2 months.


Contraindications have not yet been identified.


Information regarding safety and efficacy in pregnancy and lactation is lacking.


Patients taking warfarin and consuming a large quantity of food containing seaweed may experience a change in international normalized ratio because of seaweed's high vitamin K content.

Side Effects

Skin reaction, goiter, and, occasionally, intestinal effects may occur.


Excessive intake of dried seaweed may result in increased serum thyroid-stimulating hormone. There have been case reports of yellowing of the skin with excessive seaweed consumption.


1. Seaweed. Review of Natural Products. Facts & Comparisons [database online]. St. Louis, MO: Wolters Kluwer Health Inc; June 2011.

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