Skip to main content


Medically reviewed by Last updated on Mar 10, 2022.

What are other common names?

  • Ascophyllum nodosum
  • Fucus vesiculosis
  • Atlantic Kelp
  • Black Tang
  • Bladder Fucus
  • Bladder Wrack
  • Blasentang
  • Cutweed
  • Fucus
  • Kelp
  • Kelpware
  • Knotted Wrack
  • Laminaire
  • Marine Oak
  • Norwegian Seaweed
  • Ocean Kelp
  • Rockweed
  • Rockwrack
  • Sea Kelp
  • Seaweed
  • Seawrack
  • Tang
  • Varech

What is this product used for?

Bladderwrack is a type of seaweed and is used by some people as a food source. It is also sold as a dietary supplement product. Information from medical studies does not support the use of bladderwrack for any health problem.

What are the precautions when taking this product?

  • Always check with your doctor before you use a natural product. Some products may not mix well with drugs or other natural products.

  • This product may interfere with some lab tests. Be sure to talk with your doctor about this and all drugs you are taking.

  • Be sure to tell your doctor that you take this product if you are scheduled for surgery or tests.

  • Do not use this product if you are pregnant or plan to become pregnant soon. Use birth control you can trust while taking this product.

  • Do not use this product if you are breastfeeding.

  • Do not give this product to children.

  • Take extra care if you are taking drugs that contain hormones. These are drugs like birth control pills and hormone replacement therapy.

  • Take extra care if you are allergic to iodine or take drugs that increase iodine in your body.

  • Take extra care if you are taking drugs to thin your blood. These are drugs like warfarin, heparin, or enoxaparin.

  • Take extra care if you are taking drugs to dissolve blood clots. These are drugs like alteplase, reteplase, or streptokinase.

  • Take extra care if you are taking drugs to help with swelling or inflammation. These are drugs like nonsteroidal anti-inflammatory drugs (NSAIDs), aspirin, ibuprofen, or naproxen.

  • Take extra care if you are taking drugs for your thyroid. These are drugs like levothyroxine, thyroid desiccated, or liotrix.

  • Take extra care and check with your doctor if you have:

    • Thyroid problems

    • Bleeding problems

    • Diabetes

What should I watch for?

  • Upset stomach

  • Stomach cramps

  • Rash

When do I need to call the doctor?

  • Signs of a very bad reaction. These include wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat. Go to the ER right away.

  • Signs of thyroid problems. These include unexplained weight loss, fast heartbeat, or shakiness.

  • Signs of high blood pressure. These include very bad headaches, nervousness, problems breathing, or nosebleeds.

  • Swollen neck

  • Very bad throwing up

  • Very bad belly pain

  • Very bad loose stools

  • Bruising or bleeding that is not normal

  • Changes in menstrual periods like lots of bleeding, spotting, or bleeding between cycles

Last Reviewed Date


Consumer information use

This generalized information is a limited summary of diagnosis, treatment, and/or medication information. It is not meant to be comprehensive and should be used as a tool to help the user understand and/or assess potential diagnostic and treatment options. It does NOT include all information about conditions, treatments, medications, side effects, or risks that may apply to a specific patient. It is not intended to be medical advice or a substitute for the medical advice, diagnosis, or treatment of a health care provider based on the health care provider's examination and assessment of a patient’s specific and unique circumstances. Patients must speak with a health care provider for complete information about their health, medical questions, and treatment options, including any risks or benefits regarding use of medications. This information does not endorse any treatments or medications as safe, effective, or approved for treating a specific patient. UpToDate, Inc. and its affiliates disclaim any warranty or liability relating to this information or the use thereof. The use of this information is governed by the Terms of Use, available at


Copyright © 2022 UpToDate, Inc. and its affiliates and/or licensors. All rights reserved.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.