The form of seaweed known as bladderwrack (Fucus vesiculosus) is an edible brown plant which grows primarily in the upper coastal regions of the United States and the Atlantic and Baltic regions of Europe. Many sources refer to bladderwrack as a type of kelp, but this is not entirely accurate. Bladderwrack often grows alongside other seaweeds, including kelp, but it is its own species. The plant derives its name from the sets of air-filled sacs or bladders which run along its center and help keep it afloat in ocean waters. Only the center stalk of the bladderwrack plant is generally used for medicinal purposes.

Because bladderwrack grows in the sea, it accumulates and concentrates various minerals and nutrients not readily found in earthbound plants. One of the most important elements found in bladderwrack is iodine, a chemical compound prized for its antiseptic properties and its effect on the human thyroid. As early as 1811, bladderwrack became a popular source of medicinal iodine. Eventually bladderwrack became known as a miracle plant, used to cure or treat diseases such as coughs, asthma, hemorrhoids, boils, goitres, stomach ailments, urinary infections and headaches. Not all of these bladderwrack-based treatments proved to be effective, however.

The high concentration of iodine does make bladderwrack a useful plant for legitimate medical purposes, primarily in the treatment of thyroid conditions which trigger metabolism problems. Since the bladderwrack extract improves thyroid function, a person's metabolism may also be expected to improve. A higher metabolism rate generally leads to improved weight loss, so by extension bladderwrack extract could be considered a weight-loss aid. A number of people take diet supplements containing bladderwrack extract as a way to increase their metabolic rate and digest food more efficiently.

Other products such as cosmetics and skin creams may include bladderwrack extract because of its effect on human skin. Many people have reported noticeable improvements to skin conditions such as eczema and acne after applying ointments containing bladderwrack. Some cosmetic companies even claim that regular use of bladderwrack extract can help tighten skin and reduce the appearance of wrinkles and fine lines. There appears to be some scientific evidence to back up many of these claims, although bladderwrack by itself is not considered to be a miracle plant.

Bladderwrack extract can be ordered through many natural health food and herbal medicine outlets, although it may be marketed under numerous names: Black-tang, bladder, bladder fucus, Blasen-tang, brown algae, common seawrack, cut weed, Dyers fucus, edible seaweed, fucoidan, fucoxantin, Fucus, green algae, Hai-ts'ao, kelp, kelpware, knotted wrack, Meereiche, Quercus marina, popping wrack, red algae, red fucus, rockrack, rockweed, schweintang, sea kelp, sea oak, seetang, seaware, seaweed, sea wrack, swine tang, tang, Varech vesiculeux, vraic, and wrack.