Because sea moss is high in iodine, taking it excessively could lead to thyroid problems, including goiter and hyper- or hypothyroidism. Excessive iodine intake can also cause stomach upset, fever, and burning in the throat or mouth.National Institutes of Health. (2022). Iodine - Fact Sheet for Consumers. NIH. Because sea moss absorbs heavy metals when it grows, you may consume some when taking a supplement.Lomartire, S., Marques, J. C., & Gonçalves, A. M. M. (2021). An Overview to the Health Benefits of Seaweeds Consumption. Marine Drugs, 19(6), 341. (To avoid contaminants like this, choose a product that provides third-party testing results.) Toxic levels of heavy metals can cause kidney and immune system problems, among other symptoms. Sea moss may also act as an anticoagulant, so be cautious if you have a bleeding disorder or take blood thinners.Adrien, A., Dufour, D., Baudouin, S., Maugard, T., & Bridiau, N. (2017). Evaluation of the anticoagulant potential of polysaccharide-rich fractions extracted from macroalgae. Natural Product Research, 31(18), 2126–2136. It’s best to consume sea moss supplements in moderation, according to the dosing instructions, and under the supervision of a physician.