Bladder wrack
Bladder wrack
This information describes the common uses of Bladder wrack, how it works, and its possible side effects.

Common Name

Sea kelp, Brown kelp seaweed, Sea wrack, Marine oak

How It Works

Claims of beneficial effects of bladder wrack have not been confirmed in clinical studies.

Bladder wrack extract is rich in iodine and is claimed to stimulate thyroid activity to treat obesity. There is no evidence to support this. Women who took bladder wrack showed improvement in their menstrual symptoms. Topical application of a bladder wrack extract showed benefits for skin. Further studies are needed to confirm 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.

Purported Uses

  • Weight loss
    Evidence is lacking to support this claim.
  • Skin care
    Results of a small clinical study showed that topical bladder wrack extract can improve the elasticity of skin.
  • Hypothyroidism
    Bladder wrack is rich in iodine and has been used as a supplement for patients with hypothyroidism caused by iodine deficiency. However, this has not been studied in clinical trials and the dosage used is unclear.
  • Fatigue
    Evidence is lacking to support this claim.
  • Menstrual abnormalities
    In a small study, women who took bladder wrack reported improvement in menstrual symptoms.

Patient Warnings

Consumption of bladder wrack harvested from polluted waters may cause kidney toxicity due to the presence of heavy metals such as arsenic, cadmium and mercury.

Do Not Take If

  • If you are taking Cytochrome P450 substrates: Bladder wrack inhibits cytochrome P450 enzymes, thereby affecting the cellular concentration of drugs that are metabolized by these enzymes. Clinical relevance is not known.
  • If you are taking Amiodarone: Bladder wrack decreased the bioavailability of amiodarone (used to treat arrhythmia) in a murine model. Clinical relevance is not known.

Side Effects

  • Consumption of a slimming product containing 20 different herbs, bladder wrack being one of them, resulted in hemorrhagic cystitis (inflammation of the urinary bladder) in a 33-year-old woman. Symptoms resolved after discontinuing the product.