Bladderwrack (Kelp) is a laxative and contains considerable amounts of iodine. Given its iodine content, it has been used to regulate low thyroid function due to a lack of iodine in the diet (hypothyroidism). Bladderwrack has also been proposed as a weight-loss agent. Herbalists rely on kelp’s active ingredient, sodium alginate, to treat heavy-metal toxins such as barium and cadmium, and to prevent the body from absorbing strontium-90, a radioactive substance created in nuclear power plants. Besides iodine, kelp has an enormous supply of essential nutrients, including protein, essential fatty acids, fibre, sodium and potassium salts, and a variety of other substances. The trace mineral content of kelp is among the highest of any single known source.

Botanical Name

Fucus vesiculosus

Part Used


Common Names

Seawrack, kelpware, kelp, black-tang, bladder fucus, cutweed, rockweed, Fucus, Quercus marina, Cutweed, Fucus (Varech) vesiculeux, Blasentang, Seetang.

Brief History

Fucus vesiculosusBladderwrack has been employed as a fuel, as a winter feed for cattle, and as a source of iodine and potash. It has been used medicinally since antiquity. Iodine was first discovered by distillation of Fucus in the early nineteenth century, and for about 50 years most commercial supplies of Iodine were obtained in this way. Its common name is derived both from the typical bladder-like air vesicles on the thallus and from an ancient word signifying something which is driven ashore.


Triterpene glycosides (acetein, cimicifugoside, racemoside), isoflavones, aromatic acids (isoferulic acid, salicylic acid), tannin, resins (cimicifugin), ranunculin, fatty acids, tannins, starch, sugars

Therapeutic Properties

Metabolic Stimulant, Antiobesity, antirheumatic, thyroid stimulant.

Vitalist Properties

Temperature: Cool

Moisture: Moist

Therapeutic Indications

Rheumatism, rheumatoid arthritis, reduced thyroid function to assist weight loss.

Primary Uses

Underactive Thyroid

Bladderwrack has proved useful in the treatment of underactive thyroid and goitre. By regulating thyroid function, the seaweed helps bring about improvement in all related symptoms.

Cancer prevention and PMS

Kelp has been demonstrated to have anti-estrogenic effects. It is believed to be responsible for the reduced risk of estrogen-related cancers in Asian populations. It also may lower estradiol levels, thereby altering menstrual cycle patterns. In a study using rats, kelp acted as a competitive inhibitor of estradiol, thereby lengthening the oestrous cycles of the rats.

Cellulite and Skin Elasticity

When applied topically, kelp acts as an anti-collagenase and antioxidant, which improve the skin’s elasticity and keeps it supple and may address cellulite.


Bladderwrack is a gentle laxative. Up to 25 percent of its weight consists of algin, a complex carbohydrate that swells in water. Algin forms a gel within the intestines that coats and soothes the intestinal lining and softens the stool.

Clinical Research

  • Experimental studies conducted and reported in 1910 found oral doses of bladderwrack have a stimulatory activity on the thyroid gland.
  • In a controlled clinical trial, obese volunteers taking bladderwrack extract in addition to a controlled diet achieved a significantly higher average weight loss than did those on a diet alone.

Dosage (Divided Daily)

Dried Powder: 1,500 – 6,000mg

• Liquid Extract: 4.5 – 8.5mL (1:1 liquid extract)

Buy Bladderwrack Capsules & Loose Powder
Dried Bladderwrack


Hyperthyroidism, pregnancy, lactation, and cardiac problems associated with hyperthyroidism.

Side effects

Kelp’s iodine content may cause hyper- or hypothyroidism, and it may interfere with existing treatment for abnormal thyroid function. In general, brown seaweeds are known to concentrate various heavy metals and other toxic elements. Elevated urinary arsenic concentrations have been traced to ingestion of kelp tablets. Prolonged intake of kelp may reduce gastrointestinal iron absorption (due to the binding properties of fucoidan), resulting in a slow reduction in haemoglobin, packed cell volume, and serum iron concentrations. Prolonged ingestion may also affect the absorption of sodium and potassium ions (alginic acid) and cause diarrhoea.

Interactions with other drugs

Bladderwrack may interact with thyroid replacement therapies (thyroxine).


  1. Balch, P. A., & Bell, S. J. (2012). Prescription for herbal healing (2nd ed.). New York, N.Y.: Avery.

  2. Bone, K. (2003). A clinical guide to blending liquid herbs: herbal formulations for the individual patient. St. Louis, MI: Churchill Livingstone.
  3. Herbalpedia (2013)
  4. Hoffmann, D. (2003). Medical herbalism: the science and practice of herbal medicine. Rochester, Vt.: Healing Arts Press.
  5. Mars, B. (2007). The desktop guide to herbal medicine: the ultimate multidisciplinary reference to the amazing realm of healing plants, in a quick-study, one-stop guide. Laguna Beach, CA: Basic Health Pub. 

All material on this website is provided for your information only and may not be construed as medical advice or instruction. No action or inaction should be taken based solely on the contents of this information; instead, readers should consult appropriate health professionals on any matter relating to their health and well-being.

Share your experience with this herb.

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.