Health Guide


What is it?

Fucus is an herbal medicine used to treat high cholesterol, arthritis, rheumatism (sore aching joints), and low thyroid hormones.

Other names for Fucus include: Black Twang, Bladderwrack, Kelp, Rockweed, Fucus vesiculosus, and Seawrack.

Ask your doctor, nurse, or pharmacist if you need more information about this medicine or if any information in this leaflet concerns you.

Before Using:

Tell your doctor if you

  • are taking medicine or are allergic to any medicine (prescription or over-the-counter (OTC) or dietary supplement)
  • are pregnant or plan to become pregnant while using this medicine
  • are breastfeeding
  • have hyperthyroidism (high thyroid hormones)
  • have any other health problems, such as high blood pressure or heart or blood vessel disease


Talk with your caregiver about how much Fucus you should take. The amount depends on the strength of the medicine and the reason you are taking Fucus. If you are using this medicine without instructions from your caregiver, follow the directions on the medicine bottle. Do not take more medicine or take it more often than the directions tell you to.

To store this medicine:

Keep all medicine locked up and away from children. Store medicine away from heat and direct light. Do not store your medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down and not work the way it should work. Throw away medicine that is out of date or that you do not need. Never share your medicine with others.

Drug and Food Interactions:

Do not take Fucus without talking to your doctor first if you are taking:

  • Thyroid medicine (example: levothyroxine (Synthroid(R)))


  • Before taking Fucus, tell your doctor if you are pregnant or breastfeeding
  • Do not use in children (2)
  • May cause high levels of arsenic (a poison) in the urine (2)
  • Using for too long may reduce the ability of your body to absorb (use) iron, sodium and potassium (2,3)

Side Effects:

Stop taking your medicine right away and talk to your doctor if you have any of the following side effects. Your medicine may be causing these symptoms which may mean you are allergic to it.

  • Breathing problems or tightness in your throat or chest
  • Chest pain
  • Skin hives, rash, or itchy or swollen skin

Other Side Effects:

You may have the following side effects, but this medicine may also cause other side effects. Tell your doctor if you have side effects that you think are caused by this medicine.

  • Acne (5)
  • Diarrhea (loose stools) (2)
  • Hyperthyroidism (high thyroid hormones) may occur (3)


1. Bradley PR (ed): British Herbal Compendium, Vol 1. British Herbal Medicines Association, Bournemouth, UK; 1992.

2. Newall C, Anderson L, Phillipson J. Fucus. In: Herbal Medicines: A Guide for Health Care Professionals. The Pharmaceutical Press, London, UK; 1996.

3. McGuffin M, Hobbs C, Upton R et al (eds): American Herbal Products Association's Botanical Safety Handbook: guidelines for the safe use and labeling for herbs in commerce. CRC Press, Boca Raton, FL; 1997.

4. Anon: British Herbal Pharmacopoeia. British Herbal Medicine Association, Keighley, England; 1983.

5. Harrell BL & Rudolph AH: Kelp diet: a cause of acneiform eruption. Arch Dermatol 1976; 112: 560.

Last Updated: 7/4/2018
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