Fucus vesiculosus L. · herb
Evidence tier: traditional
Bladderwrack is Fucus vesiculosus, a brown seaweed of cold rocky shores. It is named for the air bladders that keep its fronds afloat, and is dried and sold as a powder, in capsules or as a tincture.
No benefit mechanism is established in people. Bladderwrack acts through its iodine on the thyroid; higher doses can change thyroid stimulating hormone (EMA section 4.9). Its fucoidan is a strong anticoagulant in the test tube, but in a small human trial 3 g a day for 12 days showed no obvious anticoagulant effect, probably because it is poorly absorbed (PMID 19696660).
Traditional use only. The EMA registers bladderwrack solely as a traditional herbal medicine, used alongside a reduced calorie diet for weight loss in overweight adults once a doctor has excluded other causes; traditional registration rests on long use, not trials. MSK says claims of benefit have not been confirmed in clinical studies, and in osteoarthritis it was no better than placebo. Its iodine is the active and the risk: the EMA caps total iodine from Fucus products at 400 micrograms a day.
The only authority dose is the EMA traditional posology: 130 mg of powdered herb twice a day, 2 hours before meals, with water; see a doctor if there is no weight loss after 10 weeks. Total iodine from the product must stay at or below 400 micrograms a day (EMA).
Do not combine with thyroid medicine, iodine supplements, other seaweeds or other Fucus products [EMA 4.4]. Not with amiodarone or lithium unless your doctor agrees [MSK; EMA 4.5]. Stop and see your doctor if you get palpitations, a fast heartbeat, trembling or acne [EMA 4.9].
Sea moss and bladderwrack are seaweeds, and seaweed carries iodine. The amount varies a lot, and it is not something a label can tell you reliably. If you have a thyroid condition, take thyroid medication, or have Hashimoto's, do not take this without talking to your doctor first. Do not take it if you are pregnant or breastfeeding.
Pregnancy: avoid
Breastfeeding: avoid
Active compounds: iodine, fucoidan (sulfated polysaccharide), fucosterol, phlorotannins
Remedies using Bladderwrack · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.