Side effects of fucus vesiculosus supplement

Updated February 21, 2017

Fucus vesiculosus, or bladderwrack, is a type of seaweed used as an herbal remedy for numerous medical conditions, including arthritis, obesity, respiratory issues, and circulatory and thyroid problems. Bladderwrack may also be applied to the skin to treat burns, insect bites and other skin problems. Its primary effective component is iodine. Like many other herbal remedies and supplements, bladderwrack can have some unpleasant side effects.


Bladderwrack is used to treat both high and low thyroid hormone conditions, but may actually cause thyroid problems if used to excess. This plan can contain high concentrations of iodine. Taking a significant amount of iodine over a long period of time may cause a goitre, or swelling of the thyroid gland, and create an increased risk of thyroid cancer.

Heavy Metal Poisoning

Because bladderwrack is harvested from the ocean, it has a chance of being contaminated with heavy metals and other poisons. Sea plants can absorb substances such as arsenic from the seawater and concentrate them. Over time, heavy metals build up in the body and can cause brain damage, kidney and nerve toxicity, abnormal bleeding, cancer and many other serious medical conditions.


According to the National Institutes of Health, bladderwrack may also cause hypoglycaemia, or low blood sugar. Patients who have hypoglycaemic or diabetic conditions, or those already taking drugs or supplements that affect blood glucose levels, should take Fucus vesiculosus with caution. It may be necessary to adjust the dose to avoid blood sugar problems.

Blood Thinning

Bladderwrack supplements have been reported to cause abnormal bleeding, minor haemorrhages and low platelet counts in some patients. People who already have bleeding disorders, or who are taking drugs that might increase their risk of bleeding, should consult with a doctor before taking this supplement. As with people at risk of hypoglycaemia, some dosage adjustments may be required. According to WebMD, bladderwrack may slow clotting and should not be taken for at least two weeks before surgery.


Bladderwrack and other brown seaweeds contain a substance called alginic acid, which is present in many laxative agents. Routine use of bladderwrack supplements may cause diarrhoea or other digestive problems.

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About the Author

G.D. Palmer is a freelance writer and illustrator living in Milwaukee, Wis. She has been producing print and Web content for various organizations since 1998 and has been freelancing full-time since 2007. Palmer holds a Bachelor of Arts degree in writing and studio art from Beloit College in Beloit, Wis.