Bladderwrack is also known by the names Black Tang, Rockweed, Bladder Fucus, Seawrack, Sea Oak, Black Tany, Cut Weed, and Rockwrack. 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. Primary chemical constituents of this plant include mucilage, algin, mannitol, beta-carotene, zeaxanthin, iodine, bromine, potassium, volatile oils, and many other minerals. The main use of Bladderwrack (and other types of seaweed) in herbal medicine is as a source of iodine, an essential nutrient for the thyroid gland. Bladderwrack has proved most useful in the treatment of underactive thyroid glands (hypothyroidism) and goiter. Through the regulation of thyroid function, there is an improvement in all the associated symptoms. Where obesity is associated with thyroid trouble, this herb may be very helpful in reducing the excess weight. It has a reputation in helping the relief of rheumatism and rheumatoid arthritis, both used internally and as an external application upon inflamed joints.