This genus of six species of marine algae is found widely in shallow waters and on shores in the northern hemisphere, where it often forms a distinct zone. Fucus vesiculosus (bladderwrack) has conspicuous air bladders, arranged in groups of two or three along the fronds to give buoyancy. The common name "wrack" is derived from the same source as "wreck", meaning something that has been washed ashore. Bladderwrack is an important seaweed manure, soil conditioner, and high potash fertilizer, especially for potatoes. It also has a reputation for being a food supplement that improves the condition of the skin and hair and encourages weight loss by stimulating the thyroid gland. Fucus serratus (toothed wrack) is used similarly, and both are used to make kelp tablets. The discovery of iodine in the 19th century was made by distilling Fucus.

A type of brown seaweed, bladderwrack has a reputation for being a weight-loss aid. If it does help speed weight loss, its probably because bladderwrack contains high amounts of iodine, which can stimulate an underactive thyroid gland.

Leathery, olive-brown seaweed with branched, strap-like fronds, which are forked at the tips and have air bladders, usually in pairs, on either side of the thick midrib.
Common Name:
Other Names:
Black-Tang, Cutweed, Fucus, Kelp, Kelpware, Rockweed, Seawrack, Wrack.
Botanical Name:
Fucus vesiculosus
Not cultivated. Found in the wild, on unpolluted shores.
In the early nineteenth century, scientists discovered that the iodine so plentiful in the common seaweed bladderwrack—or kelp, as it is usually called today—was the treatment of choice for goiter, an enlargement of the thyroid gland.  Beach-loving children and adults alike have long been familiar with this ubiquitous muddy-green seaweed—found up and down the North Atlantic shoreline—and its poppable, bladderlike, "bubbles".  Few people know, however, that seaweed is a super food, rich in potassium, calcium, magnesium, selenium, manganese, phosphorus, vitamins A and C, and the vitamin B complex.  In fact, it is a staple food product in China, Denmark, Iceland, Ireland, Japan, and Wales.
Plants are collected in summer, when the nutrient content is highest; washed up plants are not suitable for medicinal use, having lost important nutrients. They are dried in thin layers, being turned regularly; when brittle, the blackish brown strips are chopped and ground. As a fertilizer, it is spread fresh or dried, directly onto the soil and dug in, rather than being composted in piles. Small amounts are also added to compost piles as an activator.
Native Region:
The Atlantic, English Channel, North Sea, and Baltic.
15cm-1m (6-36in)
7.5-50cm (3-20in)
Not applicable
Parts Used:
Whole plant, Thallas (plant body), Fronds.
A mucilaginous, salty, tonic herb that stimulates the thyroid, helps control weight, and had antibiotic effects.
Vitamin Content:
Medicinal Uses:
Internally for goiter and obesity that is associated with thyroid deficiency. Excess may overstimulate the thyroid, leading to thyrotoxicosis. Contraindicated during pregnancy and lactation, and in overactive thyroid. Externally for rheumatic complaints.
To treat obesity, arteriosclerosis, digestive disorders, diseases of the thyroid, and sprains.
Traditional herbalists still use bladderwrack/kelp to treat goiter as well as hypothyroidism—a condition caused by an underactive thyroid that is characterized by low energy, fatigue, sleep disturbances, and weight gain.  Bladderwrack is a mild stimulant and tonic, and it is frequently prescribed to boost energy levels and to promote weight loss.  It is also taken to offset the effects on the body of environmental and heavy-metal pollutants.
Typical Dose:
A typical dose of bladderwrack may range from 5 to 10gm in the form of an infusion, taken three times daily, or 4 to 8ml of extract, taken three times daily.
Fresh bladderwrack/kelp may be eaten raw—by itself in salads—or cooked in soups and vegetable dishes.  Dried bladderwrack/kelp may be sprinkled on foods or taken in tablet form.  It is available fresh in specialty food stores and health food markets, and widely available in dried bulk, powdered herb, and tablets in health food stores, herb shops, pharmacies, and supermarkets.
Possible Side Effects:
Bladderwrack's more common side effects include acne, allergic reactions, and triggering or worsening hyperthyroidism.
Drug Interactions:
Taking bladderwrack with these drugs may increase the risk of bleeding or bruising:
Abciximab, (ReoPro)
Alteplase, (Activase, Cathflo Activase)
Antithrombin III, (Thrombate III)
Argatroban, (Argatroban)
Aspirin, (Bufferin, Ecotrin)
Aspirin and Dipyridamole, (Aggrenox)
Bivalirudin, (Angiomax)
Clopidogrel, (Plavix)
Dalteparin, (Fragmin)
Danaparoid, (Orgaran)
Dipyridamole, (Novo-Dipiradol, Persantine)
Enoxaparin, (Lovenox)
Eptifibatide, (Integrillin)
Fondaparinux, (Arixtra)
Heparin, (Hepalean, Hep-Lock)
Indobufen, (Ibustrin)
Lepirudin, (Refludan)
Nadroparin, (Fraxiparine)
Reteplase, (Retavase)
Streptokinase, (Streptase)
Tenecteplase, (TNKase)
Ticlopidine, (Alti-Ticlopidine, Ticlid)
Tinzaparin, (Innohep)
Tirofiban, (Aggrastat)
Urokinase, (Abbokinase)
Warfarin, (Coumadin, Jantoven)
Taking bladderwrack with these drugs may reduce the effectiveness of the drug:
Acetazolamide, (Apo-Acetazolamide, Diamox Sequels)
Amiloride, (Midamor)
Azosemide, (Diat)
Bumetanide, (Bumex, Burinex)
Chlorothiazide, (Diuril)
Chlorthalidone, (Apo-Clorthalidone, Thalitone)
Ethacrynic Acid, (Edecrin)
Etozolin, (Elkapin)
Furosemide, (Apo-Furosemide, Lasix)
Hydrochlorothiazide, (Apo-Hydro, Microzide)
Hydrochlorthiazide and Triamterene, (Dyazide, Maxzide)
Hydroflumethiazide, (Diucardin, Saluron)
Indapamide, (Lozol, Nu-Indapamide)
Levothyroxine, (Synthroid, Levothroid)
Liothyronine, (Cytomel, Triostat)
Liotrix, (Thyrolar)
Mannitol, (Osmitrol, Resectisol)
Mefruside, (Baycaron)
Methazolamide, (Apo-Methazolamide, Neptazane)
Methyclothiazide, (Aquatensen, Enduron)
Metolazone, (Mykrox, Zaroxolyn)
Olmesartan and Hydrochlorothiazide, (Benicar HCT)
Polythiazide, (Renese)
Spironolactone, (Aldactone, Novo-Spiroton)
Thyroid, (Nature-Thyroid NT, Westhroid)
Torsemide, (Demadex)
Triamterene, (Dyrenium)
Trichlormethiazide, (Metatensin, Naqua)
Urea, (Amino-Cerv, Ultramide)
Xipamide, (Diurexan, Lumitens)
Taking bladderwrack with these drugs may increase the risk of hypoglycemia (low blood sugar):
Acarbose, (Prandase, Precose)
Acetohexamide, (Acetohexamide)
Chlorpropamide, (Diabinese, Novo-Propamide)
Gliclazide, (Diamicron, Novo-Gliclazide)
Glimepiride, (Amaryl)
Glipizide, (Glucotrol)
Glipizide and Metformin, (Metaglip)
Gliquidone, (Beglynor, Glurenorm)
Glyburide, (DiaBeta, Glynase)
Glyburide and Metformin, (Glucovance)
Insulin, (Humulin, Novolin R)
Metformin, (Glucophage, Riomet)
Miglitol, (Glyset)
Nateglinide, (Starlix)
Pioglitazone, (Actos)
Repaglinide, (GlucoNorm, Prandin)
Rosiglitazone, (Avandia)
Rosiglitazone and Metformin, (Avandamet)
Tolazamide, (Tolinase)
Tolbutamide, (Apo-Tolbutamide, Tol-Tab)
Disease Effects:
  • May worsen cases of acne.
  • May worsen hyperthyroidism.
  • May worsen iron deficiency by hindering the body's ability to absorb iron.
If you suspect that you have a thyroid problem, or if you have a history of thyroid ailments, consult your doctor first before self-treating with bladderwrack/kelp.  If you are already taking medication for an overactive thyroid (hyperthyroidism), bladderwrack/kelp can worsen this condition since it stimulates the thyroid gland.  The herb also contains a  high sodium content.  If you are on a salt-restricted diet, therefore, and/or have high blood pressure, avoid using the herb.
Culinary Uses:
Plants are steamed or boiled in cheesecloth bags (removed before serving) with seafood or vegetables to give a sweet, salty flavor, as in New England clambakes.
Economic Uses:
Used for ferilizers, livestock feed, and mineral supplements, and as a source of iodine. Source of alginates for the food, textile, cosmetic, and pharmaceutical industries.
Encyclopedia of Herbs by Deni Brown Copyright © 1995, 2001 Dorling Kindersley Limited. pg. 217
The Essential Herb-Drug-Vitamin Interaction Guide by Geo. T. Grossberg, MD and Barry Fox,PhD Copyright©2007 Barry Fox,PhD. Pp.84-86
The Modern Herbal Primer by Nancy Burke Copyright©2000 Yankee Publishing, Inc. pg 13.