Bladderwrack
Bladderwrack (Fucus vesiculosus) is a brown seaweed from the coasts of the North Atlantic and Baltic Sea that naturally contains iodine.
Also listed as Fucus Vesiculosis, Organic Bladderwrack, Bladderwrack Powder, Bladderwrack Extract
What it is studied for
The strongest rated effects first. Bars show the size of the effect, the letter grades the evidence, and each rating lists the studies behind it.
Can a seaweed supplement help with weight?
Bladderwrack is Fucus vesiculosus. EMA recognizes a traditional use for powdered bladderwrack alongside a reduced-calorie diet in overweight adults, after a doctor has excluded serious underlying conditions. This recognition rests on long-standing use, not convincing clinical evidence of weight loss. 1
Why iodine changes the conversation
Bladderwrack contains iodine, and excessive doses can alter thyroid-related laboratory values and cause palpitations or trembling. That makes an iodine-containing seaweed a poor basis for guessing how to manage a thyroid problem. EMA specifically warns against combining it with thyroid medicines or other iodine preparations. 2
Why people take it
SuppCo community snapshot, 2026-09-28. Reasons for use are not evidence that it works.
Questions people ask
Is bladderwrack a proven weight-loss treatment?
No. EMA’s traditional-use indication is explicitly based on long-standing use rather than sufficient clinical trials. 1
Can it be taken with thyroid medication?
EMA says not to combine bladderwrack medicines with medicines for the thyroid or other iodine preparations. 2
Does it prevent a blood-sugar spike?
The single-meal trial in healthy adults found no improvement in glucose or insulin responses at either tested dose. It does not answer every possible long-term use. 3
Does the 400-microgram limit tell me how much iodine I need?
No. It is the EMA monograph’s limit for iodine supplied by Fucus-containing medicines, not an individual requirement. 2