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Fucus vesiculosus is a seaweed 1. You might be more familiar with its common name, which is bladderwrack, according to Natural Standard 12. It is sometimes used as an herbal medicine, according to the National Institutes of Health (NIH). You may see it advertised as a treatment for thyroid issues, asthma, coughs, stomach problems, urinary diseases, as a way to prevent headaches, as a preventive measure for tumors or ulcers or as a weight loss aid. There is not enough research to recommend for or against any of these uses, advises NIH. Meanwhile, there are possible side effects of which you should be aware.
If you are experiencing serious medical symptoms, seek emergency treatment immediately.
Iodine and Heavy Metal Toxicity
Most of the side effects you might experience are related to Fucus vesiculosus's high iodine content, or to contamination of bladderwrack preparations by heavy metals or other substances, advises NIH 12. In fact, NIH advises that consuming bladderwrack is considered “potentially unsafe” due to potential contamination 2. Iodine toxicity can cause abnormal thyroid conditions. Bladderwrack theoretically can decrease or increase blood thyroid hormone levels 2. High iodine levels can also lead to acne-type skin lesions, stomach irritation, a brassy taste in your mouth, or increased salivation. Arsenic contamination of seaweed has led to nerve and kidney toxicity in some people. Contamination also can lead to abnormal bleeding and reduced blood platelet count.
- Most of the side effects you might experience are related to Fucus vesiculosus's high iodine content, or to contamination of bladderwrack preparations by heavy metals or other substances, advises NIH 1.
- Arsenic contamination of seaweed has led to nerve and kidney toxicity in some people.
Lower Blood Sugar Levels
What Supplements & Herbs Interact With Hydrochlorothiazide?
Fucus vesiculosus extracts can lower blood sugar 1. The NIH urges caution for people who have hypoglycemia, diabetes, or who take herbs or drugs that affect blood-sugar levels. It’s best to have your serum glucose levels monitored by a doctor if taking bladderwrack, according to NIH 2.
There are potential blood-thinning, or anticoagulant, properties in bladderwrack 2. There are reports of autoimmune thrombocytopenic purpura in people consuming this seaweed, according to NIH. If you take blood thinners or other drugs that can increase risk for bleeding, or have a bleeding disorder, you need to be monitored by a doctor when taking Fucus vesiculosus, NIH advises.
Kelp Overdose Symptoms
The alginic acid in Fucus vesiculosus may cause a laxative effect, according to NIH. This effect most often is experienced with chronic use the seaweed. Combining bladderwrack with other laxatives may boost the effect of those laxatives 2.
If you take drugs for your thyroid, bladderwrack may interfere with their function due to its high iodine content, according to NIH 2. If you take lithium, take care. Using iodine-containing agents can alter thyroid function when taken along with this drug. Also be cautious if you take hormonal drugs, including birth control, because bladderwrack may interact with these 2.
Due to lack of reliable scientific information on Fucus vesiculosus, you should avoid it if you are pregnant or breastfeeding, according to RX List. You need to be concerned about its high iodine levels and possible heavy metal contamination, according to NIH.
What Supplements & Herbs Interact With Hydrochlorothiazide?
Kelp Overdose Symptoms
Fucus Vesiculosus Uses
How to Take Kelp Powder
What Are the Health Benefits of Kelp for High Blood Pressure & Cholesterol?
Thyroid Shrinking With Herbs
Can I Eat Seaweed If I Have Hyperthyroidism?
The Side Effects of Agnus Castus
Side Effects of Kelp Tablets
Negative Side Effects of Royal Maca
- Natural Standard: Seaweed, kelp, bladderwrack (Fucus vesiculosus)
- RXList: Bladderwrack
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- Catarino Marcelo D, Silva Artur MS, Cardoso Susana M. Phycochemical Constituents and Biological Activities of Fucus spp. Mar Drugs. 2018 Aug; 16(8): 249.
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- Fujimura T, et al. Treatment of human skin with an extract of Fucus vesiculosus changes its thickness and mechanical properties. J Cosmet Sci. 2002 Jan-Feb;53(1):1-9.
- Haskell-Ramsay Crystal F, et al. Acute Post-Prandial Cognitive Effects of Brown Seaweed Extract in Humans. Nutrients. 2018 Jan; 10(1): 85.
- Kim Jae-Young, et al. Effects of the Brown Seaweed Laminaria japonica Supplementation on Serum Concentrations of IgG, Triglycerides, and Cholesterol, and Intestinal Microbiota Composition in Rats. Front. Nutr., 12 April 2018.
- Memorial Sloan-Kettering Cancer Center. About herbs: Bladder wrack.
- Myers Stephen P, et al. A combined phase I and II open label study on the effects of a seaweed extract nutrient complex on osteoarthritis. Biologics. 2010; 4: 33–44.
- National Institutes of Health. MedlinePlus Supplements. Fucus Vesiculosus.
- Paradis ME, Couture P, Lamarche B. A randomised crossover placebo-controlled trial investigating the effect of brown seaweed (Ascophyllum nodosum and Fucus vesiculosus) on post-challenge plasma glucose and insulin levels in men and women. Appl. Physiol. Nutr. Metab. 2011;36:913–919.
- Romm, Aviva. "Botanical Medicine for Women’s Health."
- Sharifuddin Yussrizam, et al. Potential Bioactive Compounds from Seaweed for Diabetes Management. Mar Drugs. 2015 Aug; 13(8): 5447–5491.
- Skibola CF. The effect of Fucus vesiculosus, an edible brown seaweed, upon menstrual cycle length and hormonal status in three pre-menopausal women: a case report. BMC Complement Altern Med. 2004 4;4:10.
- Skibola Christine F, et al. Brown Kelp Modulates Endocrine Hormones in Female Sprague-Dawley Rats and in Human Luteinized Granulosa Cells. The Journal of Nutrition, Volume 135, Issue 2, February 2005, Pages 296–300.
- Ventura S, Rodrigues M, Falcao A, Alves G. Safety evidence on the administration of Fucus vesiculosus L. (bladderwrack) extract and lamotrigine: data from pharmacokinetic studies in the rat. Drug Chem Toxicol. 2018 Oct 18:1-7.
Linda Tarr Kent is a reporter and editor with more than 20 years experience at Gannett Company Inc., The McClatchy Company, Sound Publishing Inc., Mach Publishing, MomFit The Movement and other companies. Her area of expertise is health and fitness. She is a Bosu fitness and stand-up paddle surfing instructor. Kent holds a bachelor's degree in journalism from Washington State University.