Claims of benefit with use of bladder wrack have not been confirmed in clinical studies.
Bladder wrack extract is rich in iodine. Although it is claimed to stimulate thyroid activity to treat obesity, there is no evidence to support this, and data in humans are quite limited.
In one small study, women who took bladder wrack showed improvement in their menstrual symptoms. Other small studies showed only marginal impacts on metabolic and inflammatory responses and that it was no more effective than placebo for osteoarthritis. Topical application of a bladder wrack extract suggest benefits for skin, but further studies are needed to confirm any of these effects.
Bladder wrack is often referred to as brown kelp but it should not be confused with "kelp," which is another species of seaweed.