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Overview: Fucus vesiculosus, or bladderwrack, is a type of brown seaweed. It is often eaten as a food, and it is also available as a dietary supplement. People take these supplements for many reasons, but their benefits are not well defined. The most common side effect is an upset stomach. Before taking Fucus vesiculosus, make sure to tell your health care provider about all of your health conditions and any medicines or supplements you may be using. In particular, tell your health care provider if you have thyroid problems or are taking any products that contain iodine.

Uses

What is Fucus vesiculosus used for?

Fucus vesiculosus is used for various reasons, but its benefits for any use are not well defined. Some common reasons for using Fucus vesiculosus include the following.

Note: The FDA has not reviewed Fucus vesiculosus for safety and effectiveness. Learn more about dietary supplements here.

How does Fucus vesiculosus work (mechanism of action)?

Fucus vesiculosus, also known as bladderwrack, is a type of brown seaweed. The name bladderwrack comes from the small pockets of air in its leaves (fronds). These pockets of air, which look like bladders, help the seaweed float. Fucus vesiculosus is sometimes referred to as “kelp,” but it is actually a different type of brown seaweed from what is most commonly called kelp.

Brown seaweeds such as Fucus vesiculosus are rich in iodine, phlorotannins, and various other nutrients, including protein and fiber. They are often eaten as foods and may also be used to make dietary supplements. Some people use Fucus vesiculosus supplements as an extra source of nutrients.

Some of the chemicals in Fucus vesiculosus may have effects in the gut. Certain complex carbohydrates, such as alginate and fucoidan, may bind to cholesterol in the gut, reducing how much cholesterol your body absorbs. Other chemicals may slow the breakdown of sugars in the gut, reducing how much sugar your body absorbs. Together, these effects may help with weight loss and lowering cholesterol and blood sugar levels. But the benefits of Fucus vesiculosus supplements for these uses are not well defined.

Fucus vesiculosus can contain very large amounts of iodine, depending on where it was grown and how the product was processed. Iodine is a mineral that your thyroid uses to make thyroid hormones. In the U.S., most people get enough iodine from their diet and iodized salt. The amount of iodine found in Fucus vesiculosus may vary, and taking too much iodine can be dangerous. Speak with a health care provider if you think you need an iodine supplement.

Fucus vesiculosus naturally contains many chemicals and nutrients. The amounts of each substance in a specific product may vary. Some, none, or all of these substances may have effects on the body. These effects may change depending on how much of each substance is found in the product you are using.

How should I store Fucus vesiculosus?

You should store Fucus vesiculosus according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.

Side Effects

What are the most common side effects of Fucus vesiculosus?

The most common side effect of Fucus vesiculosus is an upset stomach. Side effects may vary depending on the dose you are taking or the specific product you are using. Tell your health care provider if you have any side effects that bother you.

There may be other side effects of Fucus vesiculosus that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of Fucus vesiculosus?

While less common, the most serious side effects of Fucus vesiculosus are described below, along with what to do if they happen.

Severe Allergic Reactions.Fucus vesiculosus may cause allergic reactions, which can be serious. Stop taking Fucus vesiculosus and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching or skin rash
  • Bumps on the skin calledhives that can be red, pink, white, or brown depending on your skin tone
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Thyroid Problems. Fucus vesiculosus contains iodine. Large amounts of iodine can cause the function of your thyroid gland to change. This can raise your thyroid hormone levels (hyperthyroidism), lower your thyroid hormone levels (hypothyroidism), or cause your thyroid to grow larger (thyroid goiter). These problems are more likely to happen when iodine is taken regularly at doses higher than the recommended daily intake. Tell your health care provider if you have any of the following signs of thyroid problems.

  • Weight gain or weight loss
  • Feeling unusually cold or hot
  • Tiredness that does not go away or continues to worsen
  • Mood swings
  • Trouble sleeping
  • Constipation
  • Tightness in your throat
  • A hoarse voice

Iodine Poisoning. Fucus vesiculosus contains iodine. People who regularly take large amounts of iodine may develop iodine poisoning. This is sometimes called iodism. To reduce the risk of getting iodine poisoning, do not take more iodine than the recommended daily intake or the amount recommended by your health care provider. Stop taking Fucus vesiculosus and call your health care provider right away if you have any of the following symptoms of iodine poisoning.

  • Sore gums or teeth
  • Bad headaches
  • The whites of your eyes seem red
  • Swollen eyelids
  • Blurry vision
  • Your eyes water, your nose runs, or you have more saliva in your mouth than usual

Warnings & Precautions

Who should not use Fucus vesiculosus?

Allergies to Ingredients. People who are allergic to any of the following should not take Fucus vesiculosus.

  • Bladderwrack
  • Fucus vesiculosus
  • Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific Fucus vesiculosus products they stock.

What should I know about Fucus vesiculosus before using it?

Fucus vesiculosus is a dietary supplement. It cannot be marketed to treat or cure a disease.

Read and follow the directions on the specific product you are taking, or take it as recommended by your health care provider.

Keep Fucus vesiculosus out of the reach of children.

Fucus vesiculosus contains iodine. You can get iodine from many places, including foods and vitamins or supplements. Many multivitamin and combination supplement products have iodine in them. It is important not to take too much iodine, as it can be harmful. If you are not sure how much iodine you need, talk to your health care provider.

Herbal products, such as Fucus vesiculosus, naturally contain many different chemicals. The amount of each chemical in a specific Fucus vesiculosus product can change for many reasons, including the waters where the seaweed grew, the weather during growth, the time of year when it was harvested, and the way it was processed after harvesting. If you switch to a new bottle or a different brand, you may not have the same effects or side effects because of this variability. Talk to your health care provider if you have questions or concerns.

Fucus vesiculosus is available in different forms, including liquid extracts, dried ground powder, and capsules. Each of these forms may contain different amounts of the chemicals that are naturally found in the seaweed.

Fucus vesiculosus may absorb toxic substances from the waters where it grows. These toxic substances, which include arsenic, mercury, and lead, may be found in some Fucus vesiculosus dietary supplements. The FDA has not tested Fucus vesiculosus products to confirm that they contain the ingredients stated on their labels. Some dietary supplements have been tested by third-party organizations to confirm that they contain the ingredients listed on their labels and do not contain any harmful chemicals. Learn more about how to choose a safe dietary supplement product here.

What should I tell my health care provider before using Fucus vesiculosus?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. Also tell them if you have an upcoming surgery planned. Sharing this information will help your health care provider know if this or other supplements are right for you.

In particular, make sure that you discuss any of the following.

Thyroid Problems. Fucus vesiculosus contains iodine. Taking large amounts of iodine may change the way the thyroid works. This could make some thyroid problems worse. Tell your health care provider if you have any thyroid problems, such as high or low thyroid hormone levels, thyroid nodules, a thyroid goiter, autoimmune thyroiditis, or Graves’ disease. See the Side Effects section for more details.

Other Current and Past Health Conditions. Tell your health care provider if you have any of the following.

Other Medicines and Supplements. Fucus vesiculosus may interact with other medicines and supplements. Before taking Fucus vesiculosus, tell your health care provider about any prescription or OTC medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how Fucus vesiculosus could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. Some of the nutrients in Fucus vesiculosus, such as iodine, pass into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does Fucus vesiculosus interact with foods or drinks?

There are no known interactions between Fucus vesiculosus and foods or drinks.

It is unknown if drinking alcohol will affect Fucus vesiculosus.

Does Fucus vesiculosus interact with medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking Fucus vesiculosus.

  • A thyroid medicine, such as levothyroxine, which is used to raise thyroid hormone levels 
  • An antithyroid medicine, such as methimazole or propylthiouracil (PTU), which is used to lower thyroid hormone levels
  • Lithium, which is a medicine for certain mental health conditions
  • Any other product that contains iodine, such as iodine supplements, potassium iodide, or iodine/potassium iodide (Lugol’s solution)

The interactions between Fucus vesiculosus and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with Fucus vesiculosus is incomplete. Always check with your health care provider before taking Fucus vesiculosus with any medicines.

Overdose/Missed Dose

What should I do if I accidentally use too much Fucus vesiculosus?

If you or someone else has used too much Fucus vesiculosus, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

Read the product label closely, and speak with a health care provider about how to take Fucus vesiculosus safely. Do not take double or extra doses, even if you miss a dose.