What are the possible side effects of Seaweed, kelp, bladderwrack (Fucus vesiculosus)?

Most adverse effects appear related to high iodine content, heavy metal or other contamination of bladderwrack preparations, rather than to the seaweed itself. Because of the potential contamination of bladderwrack with heavy metals, its consumption should always been considered potentially unsafe. Based on the known effects of iodine toxicity, the high iodine content in bladderwrack may lead to abnormal thyroid conditions. In theory, bladderwrack may increase or decrease blood thyroid hormone levels. In addition, acne-type skin lesions may occur, and there are reports of severe acne exacerbations with use of kelp. Iodine may also cause a brassy taste, increased salivation, and stomach irritation. Reports of kidney and nerve toxicity have occurred in persons taking seaweed/kelp, attributed to high levels of arsenic. Abnormal bleeding and reduced blood platelet count was attributed to contaminants in a kelp product. Bladderwrack may contain vitamins and minerals, calcium, magnesium, ...  more