Side Effects of Kelp Supplements

Updated April 03, 2017

Kelp, a form of brown seaweed, is a popular dietary supplement touted for weight loss, low thyroid function, arthritis and cancer prevention. According to the National Library of Medicine, kelp supplements contain a combination of brown seaweeds such as bladderwrack. The NLM indicates some animal and human testing have shown benefits for these conditions and others, but does not consider the evidence strong enough to recommend use for these problems. Kelp, like any supplement, contains chemicals and compounds that can exert certain actions in the body, resulting in a number of side effects. Kelp’s iodine content–a trace mineral necessary for thyroid function–in particular can lead to a number of issues.


Kelp and other dietary supplements derived from the water always have the potential for contamination with heavy metals and other toxins due to harvesting from polluted water sources. According to the Physician’s Desk Reference website, there have been reports of arsenic poisoning resulting from the consumption of kelp supplements.

Thyroid Function

While kelp or other iodine supplements might help with low thyroid function, anyone with any type of thyroid problem should speak with a doctor before using kelp supplements or any supplement containing iodine. According to the University of Maryland Medical Center, excess iodine supplementation can block thyroid hormone production in people with normal thyroid function, interfere with thyroid hormone medications and increase the risk of thyroid diseases such as Grave’s disease and Hashimoto’s disease.

Other Iodine-related Conditions

The iodine level in kelp supplements can also lead to other issues. Those include acne–sometimes severe, according to the NLM–stomach irritation, metallic taste in the mouth and increased salivation. The University of Maryland Medical Center notes that excess iodine can be toxic, particularly for people suffering from kidney disease or tuberculosis.

Blood Issues

The NLM indicates kelp supplementation can affect blood sugar levels, and anyone with diabetes, low blood sugar or any other condition that requires medication to regulate levels should speak with a doctor before using kelp supplements. This supplement might also have blood-thinning properties and the NLM states there have been reports of abnormal bleeding and other bleeding disorders with this medication. Anyone with bleeding disorders or taking blood-thinning medications such as Warfarin should discuss use with a doctor.

Allergic Reaction

Conditions suggesting an allergy to the supplement include itching, hives, rash, swelling, difficulty breathing and a tightness in the throat or chest.

Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author

Kelli Cooper has been a writer since 2009, specializing in health and fitness. She holds a Bachelor of Arts in political science from Rutgers University and is a certified personal trainer with the American Council on Exercise.