Sargassum seaweed

Sargassum seaweed
Sargassum seaweed

Sargassum seaweed is a type of seaweed found along the coasts of Japan and China. Two species, Sargassum fusiforme and Sargassum pallidum, are both referred to as sargassum seaweed or gulfweed in English and hai zao in Chinese.

Sargassum seaweed is a brown algae with leafy segments supported at the surface of the ocean by air bladders. Many species of sargassum are found worldwide.

In fact, the Sargasso Sea, an area of the Caribbean near the West Indies, is named for its large floating masses of sargassum seaweed. However, sargassum used in healing is usually of Asian origin.

General use

Sargassum seaweed, or Hai zao, has been used in traditional Chinese medicine (TCM) since at least the eighth century A. D. In TCM it is characterized as having a cold nature and a salty, bitter taste.

The primary use of sargassum seaweed is to treat goiters. A goiter is a nodule in the neck caused by enlargement of the thyroid gland. The thyroid needs iodine to produce a critical hormone, thyroxin, that regulates body metabolism.

When not enough iodine is consumed in the diet, the thyroid gland enlarges. The primary natural sources of dietary iodine are sea salt, fish, and vegetables that live in the ocean.

In the days before mechanical refrigeration, it was often difficult for people living far from the ocean to get enough iodine in their diets. Today, widespread refrigeration or freezing of fish and rapid transportation to inland markets has made iodine deficiency and goiters rare in the developed world.

In addition, commercial salt manufacturers often produce a version of their product, called iodized salt, that is available in supermarkets and has iodine artificially added. However, iodine deficiency is still a worldwide problem and a major cause of mental and learning disabilities.

Using sargassum seaweed as a source of iodine to treat goiters is a scientifically sound practice. In TCM, sargassum seaweed is also used to treat such other thyroid disorders as Hashimoto’s disease.

In addition it is prescribed as a diuretic to increase the production of urine and reduce edema. It is also used to treat pain from hernia and swollen testes.

Sargassum seaweed floating around
Sargassum seaweed floating around

Sargassum seaweed is found in many common Chinese formulas. In combination with silkworm, prunella, and scrophularia, it is used to treat scrofuloderma. When sargassum seaweed is combined with water chestnut, it is used to treat silicosis, a lung disease.

Sometimes modern herbalists use sargassum seaweed to promote weight loss because it encourages the body to discharge water through the urine.

This can be risky because of the role iodine plays in setting the metabolic rate of the body. In China and Japan, fresh sargassum seaweed is sometimes stir-fried and eaten as a vegetable.

Reliable scientific evidence shows that sargassum seaweed provides enough dietary iodine to make it useful as a treatment for goiter.

There is little scientific evidence that sargassum seaweed is useful in treating such other thyroid problems as Hashimoto’s disease. Research shows that sargassum seaweed also has mild diuretic and anti-fungal properties.

Studies done in Japan (1998) and Hong Kong (2000) using different but related species of sargassum seaweed showed that sargassum seaweed contained antioxidants that helped protect the livers of rats when they were subjected to chemical damage in laboratory experiments. In general, antioxidants are thought to slow aging and protect the body from damage caused by free radicals.


Sargassum seaweed is collected from the ocean throughout the year and dried at cool temperatures away from direct sunlight for future use. This plant is a component of several Chinese formulas, including haizao yuhu tang, used to treat goiter and neixiao lei li wan, used to treat scrufuloderma. Dosage varies depending on the condition being treated.


Megafauna, such as sea turtles, large fishes and seabirds, rely upon Sargassum mats as spawning and foraging grounds, as well as nursery habitat for juveniles. Photo credit: Lindsay Martin
invasion of sargassum seaweed

Because thyroid problems are serious, people with enlarged thyroid or nodules in their neck should seek professional help from a physician and not try to treat these problems solely with alternative remedies.

Sargassum seaweed should be used with caution for weight loss because of the interactions of this product and the thyroid gland.

Side effects

No side effects have been reported when using sargassum seaweed in recommended dosages.


Some traditional Chinese herbalists claim that licorice and sargassum seaweed should not be used together; however, no scientific research supports this claim.

No interactions between sargassum seaweed and Western pharmaceuticals have bveen reported as of 2004; however, anyone taking medication for thyroid disorders should discuss the use of this remedy with their healthcare provider before using it.