Fucus vesiculosus is brown seaweed, more commonly known as bladderwrack. In parts of Asia, herbal practitioners use the seaweed medicinally to treat and prevent an array of conditions, including ulcers, goiters, urinary conditions, stomach conditions, coughs and headaches. Medicinal preparations use the plant's stem, or thallus, according to the University of California at San Diego. Although purported to treat many conditions, it has not been proven as an effective medical treatment in clinical trials, according to the National Institutes of Health. If you use it as directed, Fucus vesiculosus is generally considered safe, but you should always consult your physician before attempting any herbal remedy at home.
Thyroid Problems
Fucus vesiculosus can contain high levels of iodine. Because of this, taking bladderwrack supplements can alter a person's thyroid hormone levels, causing conditions such as hypothyroidism and hyperthyroidism, according to the National Institutes of Health.
Acne
People taking supplements containing Fucus vesiculosus may develop acne, or acne may suddenly worsen, according University of Utah Huntsman Cancer Institute. Some people have also reported developing a rash after using bladderwrack.
Laxative
Because it contains alginic acid, bladderwrack can have a laxative effect, especially when used chronically or in high doses over a long period, according to the National Institutes of Health.
Blood Mineral Levels
Using Fucus vesiculosus can alter the blood mineral levels of potassium, sodium, calcium and magnesium, according to the Huntsman Cancer Institute.
Blood Sugar Levels
People with diabetes must talk with a doctor before taking Fucus vesiculosus because it may interfere with blood sugar levels, causing them to drop too low, according to the National Institutes of Health.
Bleeding
Bladderwrack can act as a blood thinner and can cause abnormal bleeding. Because of this risk, the National Institutes of Health advises people with bleeding disorders not to take Fucus vesiculosus. The plant can also cause a low red blood cell count.
Heavy Mental Contamination
Fucus vesiculosus can grow in waters contaminated with heavy metals such as lead and arsenic. These metals are toxic and can cause serious kidney and nerve damage, according to the University of California at San Diego. To protect against these dangerous effects, look for bladderwrack products that have been harvested from clean waters.



Member Comments