Sea moss

Is sea moss safe?

It depends almost entirely on what is in the jar. Plain Irish moss (Chondrus crispus) eaten in small amounts is a mild seaweed, and a 2020 Spanish analysis found only about 3.9 milligrams of iodine per kilo of dried weed. But "sea moss" on a label can mean farmed Gracilaria or Eucheuma, and many products are blended with bladderwrack, a brown seaweed much richer in iodine. Most labels say nothing about the iodine dose.

That uncertainty is the core problem. Add arsenic and mercury found in testing, and gels recalled in 2026 for botulism risk, and sea moss ends up in the middle of our range, near ashwagandha.

Why did sea moss take off?

Mostly social media. Retail tracker SPINS, quoted by NutraIngredients in January 2026, found US sea moss sales grew from $19.5 million in 2024 to $53.3 million in 2025. The #seamoss hashtag had more than 1.5 billion TikTok views, and celebrity routines helped. Gels, gummies and capsules promise thyroid support, gut health and "92 minerals". No trial shows these benefits in people.

How much iodine is in sea moss?

Iodine varies more than any other number on the label. For context, the tolerable upper intake level for adults is 600 µg a day in the EU and 1,100 µg in the US. The American Thyroid Association advises against iodine or kelp supplements giving 500 µg a day or more.

• Plain Irish moss: low. The 2020 Spanish study calculated that an adult would need about 286 grams of dried Irish moss a day to pass the US limit.
• Seaweed supplements in general: all over the place. A 2021 Norwegian study of 96 seaweed products found supplements delivering 5 to 5,600 µg of iodine per daily dose, and one portion of 54 products would exceed the upper limit. Species and iodine labelling were often wrong or missing.
• Blends with bladderwrack or kelp: these are the ones to watch. Brown seaweeds hold far more iodine than red ones.

Germany's risk assessment agency, BfR, proposed in December 2025 that food supplements carry no more than 100 µg of iodine per daily dose. Many sea moss blends cannot show they meet that, because they never measured it.

Can sea moss cause thyroid problems?

Yes, in some people. Too much iodine can switch the thyroid off (hypothyroidism and goitre) or, in someone with an underlying condition, drive it into overdrive. A 2021 case report in the Journal of the Endocrine Society described a 28-year-old woman with a racing heart and weight loss who had been taking Irish sea moss and bladderwrack; she was found to have Graves' disease made worse by iodine. Her hormone levels improved after she stopped.

People at highest risk have thyroid nodules, Graves' or Hashimoto's disease, or a history of thyroid surgery. Ironically, they are also the people sea moss is most often marketed to.

Does sea moss contain heavy metals or bacteria?

Seaweed absorbs what is in its water. A 2026 study in the Journal of Food Protection bought 66 sea moss products from major US online retailers (53 dried, 13 gels). It found arsenic, cobalt and mercury in the dried products. It also recovered presumptive Salmonella, Cronobacter, Bacillus and Staphylococcus from both types, and gel acidity and sugar varied enormously.

Gels add a food safety problem. In January 2026 one US maker recalled 13 flavours of sea moss gel for potential Clostridium botulinum, and in April 2026 another recalled a sea moss tonic that may have been under-processed. Moist, low-acid products in sealed jars need proper processing or refrigeration.

Sea moss also contains carrageenan, the thickener. Regulators consider it safe as a food additive, and a 2026 review found the evidence on gut inflammation mixed and dependent on type and dose. It is a minor issue next to iodine.

Who should avoid sea moss or check first

• People with thyroid disease or on levothyroxine, methimazole, carbimazole or PTU.
• People taking amiodarone or lithium, which affect the thyroid themselves.
• Pregnant and breastfeeding women. LactMed advises avoiding sea moss while breastfeeding unless iodine and metals are shown to be low; a standard prenatal iodine supplement is more predictable.
• Children, whose iodine limits are lower.

If any of these apply, talk to your doctor or pharmacist before taking it.

How to choose a safer sea moss product

1. Pick a product that states iodine in µg per serving and keep total iodine from all supplements below about 500 µg a day.
2. Avoid blends with bladderwrack or kelp unless the iodine figure is given.
3. Ask for a certificate of analysis covering lead, arsenic (ideally inorganic arsenic), cadmium and mercury.
4. Treat gel as perishable. Keep it cold, follow the use-by period, and check recall lists.

How we scored it

Organ toxicity (72) and dose safety (62) reflect thyroid harm from uncertain iodine doses rather than any toxicity of Irish moss itself. Interactions (65) cover thyroid medicines, amiodarone and lithium. Product quality (42) is the weakest factor: metals, bacteria, missing iodine labels and species swaps. Regulatory actions (68) reflect the 2026 botulism recalls, with no bans.