Sea Moss and Iodine: What the Label Can't Tell You

Sea moss iodine content cannot be read from most labels, because the label usually lists how much seaweed is in a serving, not how much iodine it delivers. The NIH Office of Dietary Supplements calls seaweed one of the best food sources of iodine, and the amount varies widely. A 2021 Norwegian study that tested 96 seaweed products found 5 to 5,600 mcg of iodine per daily dose in the supplements. The U.S. adult upper limit, listed by the same NIH office, is 1,100 mcg a day.

What sea moss is, and why iodine comes up

Sea moss, also called Irish moss (Chondrus crispus), is a red seaweed. The Drugs and Lactation Database (LactMed), run by the U.S. National Institute of Child Health and Human Development, says it contains carrageenan and other carbohydrates, numerous minerals including iodine, and some toxic heavy metals such as arsenic, lead, cadmium and mercury that come from the water where it grew. Many sea moss products also contain bladderwrack (Fucus vesiculosus), a brown seaweed that LactMed describes as a kelp that contains iodine and can also contain heavy metals.

The NIH Office of Dietary Supplements calls seaweed, such as kelp, nori, kombu and wakame, one of the best food sources of iodine. The same source explains that the thyroid uses iodine to make thyroid hormones, and that both too little and too much iodine can cause problems.

Why the iodine amount is hard to know

Iodine differs a lot between seaweed species and between products. A 2021 study in Food & Nutrition Research by Aakre and colleagues bought 96 seaweed products on the Norwegian market and measured their iodine with a laboratory method called ICP-MS. The authors reported no competing interests.

Product type in the study	Iodine measured
Whole seaweed foods (43 products)	128 to 62,400 mcg per portion
Foods with added seaweed (39 products)	30 to 25,300 mcg per portion
Dietary supplements with seaweed (14 products)	5 to 5,600 mcg per daily dose

The same study found that for 54 products, one portion or dose would go above the adult upper limit the authors used, 600 mcg a day, set by the EU Scientific Committee on Food. The U.S. limit, listed by the NIH Office of Dietary Supplements, is higher, at 1,100 mcg a day. The study also reported that the seaweed species listed, and the iodine amount declared, were inadequate or inaccurate on several products. The study looked at one country's market and a limited number of supplements, so it shows how wide the range can be, not what any one product contains.

Seaweed weight is not iodine weight

A label line such as "Irish moss 500 mg" tells you how much dried seaweed is in a serving. It does not tell you the iodine in that seaweed. When a label states iodine in micrograms (mcg), you can count it. When it does not, the iodine amount is unknown from the label alone. Do not try to estimate it from general seaweed figures, because the ranges above are too wide for that.

How much iodine adults need, and the upper limit

The NIH Office of Dietary Supplements lists these Food and Nutrition Board values for adults 19 and older:

• Recommended Dietary Allowance (RDA): 150 mcg a day; 220 mcg during pregnancy; 290 mcg while breastfeeding.
• Tolerable Upper Intake Level (UL): 1,100 mcg a day, including during pregnancy and breastfeeding. The UL covers food and supplements together.

Other sources add up too. The NIH Office of Dietary Supplements says many multivitamin/mineral supplements contain iodine, often 150 mcg, and that iodine-only supplements are also sold, many in high doses, sometimes above the UL. Its food table lists 2 tablespoons of dried, flaked nori (5 g) at 116 mcg, a quarter teaspoon of iodized table salt at 78 mcg and a cup of nonfat milk at about 84 mcg. If you use a seaweed supplement, count it alongside a multivitamin, iodized salt, dairy, seafood and any other seaweed you eat.

Who should check with a healthcare provider first

The NIH Office of Dietary Supplements says high iodine intakes can cause some of the same problems as too little, including goiter, raised TSH (thyroid-stimulating hormone) and hypothyroidism. High intakes can also cause hyperthyroidism and thyroiditis. Some people, such as those with autoimmune thyroid disease, may have adverse effects at iodine intakes considered safe for the general population.

• Thyroid conditions or thyroid medicines. The same NIH sheet says high doses of iodine taken with antithyroid medicines such as methimazole can have an additive effect and could cause hypothyroidism. If you have a thyroid condition or take thyroid medication, talk with your healthcare provider before using a seaweed product.
• Certain other prescription medicines. The NIH sheet says potassium iodide taken with ACE inhibitors or potassium-sparing diuretics can raise the risk of high blood potassium. This caution is about potassium iodide; the NIH sheet does not say whether it applies to iodine from seaweed, and Seamoss+™ (the example below) lists no potassium iodide. The sheet advises anyone who takes these medicines regularly to discuss their iodine intake with their healthcare provider.
• Pregnancy and breastfeeding. LactMed says excess iodine from seaweed eaten by mothers has caused thyroid suppression in breastfed infants, and that sea moss should be avoided during breastfeeding unless its iodine and heavy metal levels have been shown to be low enough to be safe. If you are pregnant, nursing or trying to conceive, ask your healthcare provider before use.

How to read a sea moss label

• Find each seaweed and its amount. Note the species (for example Irish moss, bladderwrack) and the milligrams per serving, counting every capsule in one serving.
• Look for an iodine line. If iodine is listed in mcg, add it to your other sources and compare the total with the 1,100 mcg UL. If it is not listed, the label does not tell you the iodine dose.
• Check the other ingredients. Some formulas add roots or black pepper extract. Read the full panel and the warnings, not only the front of the bottle.
• Avoid doubling up. Using two seaweed products, or a seaweed product with a high-iodine supplement, makes it harder to know your total.

One example: Seamoss+

The Seamoss+ formula reviewed on this site lists, per two-capsule serving: Irish moss (Chondrus crispus, whole plant) 500 mg, bladderwrack (Fucus vesiculosus, whole plant) 500 mg, burdock (Arctium lappa, root) 400 mg and BioPerine black pepper extract (Piper nigrum, fruit) 5 mg. Its Supplement Facts panel gives seaweed weights and does not list an iodine amount, so the iodine per serving cannot be read from the label. The label directs two capsules once a day and adds: "For best results, take 20-30 mins before a meal or as directed by your healthcare professional."

Its product page notes that Irish moss and bladderwrack are both iodine-rich seaweeds, and that anyone with a thyroid condition, or who takes thyroid medication, should talk with a healthcare provider before starting. Its label warning reads: "Do not exceed recommended dose. Pregnant or nursing mothers, children under the age of 18, and individuals with a known medical condition should consult a physician before using this or any dietary supplement. Keep out of reach of children. Do not use if safety seal is damaged or missing. Store in a cool, dry place." LactMed (National Institute of Child Health and Human Development) says sea moss should be avoided during breastfeeding unless its iodine and heavy metal levels have been shown to be low enough to be safe; the Seamoss+ label does not list an iodine amount.

Frequently asked questions about sea moss and iodine

How much iodine is in sea moss?

It varies, and most labels do not say. In a 2021 Norwegian study of 96 seaweed products, iodine in seaweed supplements ranged from 5 to 5,600 mcg per daily dose. Only a stated iodine amount on the label tells you what a serving gives.

Is sea moss safe for your thyroid?

Iodine is needed for thyroid hormones, but too much can also cause thyroid problems, according to the NIH Office of Dietary Supplements. People with a thyroid condition, or who take thyroid medicine, should talk with a healthcare provider before using sea moss or other seaweed products.

Does bladderwrack contain iodine?

Yes. LactMed describes bladderwrack (Fucus vesiculosus) as a kelp that contains iodine and can also contain heavy metals. Many sea moss formulas include it, so count it when you read the label.

What is the upper limit for iodine?

For adults 19 and older, the Food and Nutrition Board set the tolerable upper intake level at 1,100 mcg a day from food and supplements combined, including during pregnancy and breastfeeding, as listed by the NIH Office of Dietary Supplements.

Can I take sea moss with a multivitamin?

Many multivitamins contain about 150 mcg of iodine, according to the NIH Office of Dietary Supplements. Because a sea moss label often does not list iodine, your total from both is hard to know. Ask your healthcare provider or pharmacist to review both labels.

Related reading

• Seamoss+ review
• Fish Oil Labels: EPA, DHA and Total Omega-3 Explained
• Optional next step: our supplement audit can help you organize your goals; it does not diagnose anything.

Sources

• NIH Office of Dietary Supplements: Iodine Fact Sheet for Health Professionals, updated 2024.
• Food & Nutrition Research (Aakre I, et al.): Commercially available kelp and seaweed products - valuable iodine source or risk of excess intake?, 2021.
• LactMed, National Institute of Child Health and Human Development: Sea Moss, 2026.
• LactMed, National Institute of Child Health and Human Development: Seaweed, updated 2024.

The Dose Analysis and CuraMyHealth are both operated by Hofer LLC. Purchases linked from our reviews take place on CuraMyHealth.

This article is for education and is not personal medical advice. A qualified healthcare professional can help assess your needs and review the specific formula. Individual results vary.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.