Spirulina

Is spirulina safe?

For most healthy adults taking a few grams a day of a tested product, yes. Spirulina, the dried cyanobacterium Limnospira (formerly Arthrospira) platensis, has been eaten as food for a long time, and the US Pharmacopeia gave it its top safety class, Class A, after reviewing trials and 31 adverse event reports in 2011. Health Canada licenses up to 8 g a day for adults.

The catch is the product, not the organism. Spirulina is grown in open ponds, and a pond can host other cyanobacteria that make liver toxins. Some tests also find lead. A smaller risk sits with people who have autoimmune disease, and people with PKU have to count its phenylalanine.

Microcystins: the toxin problem in blue-green algae

Microcystins are liver toxins made by cyanobacteria such as Microcystis. Spirulina does not make them, but it can be contaminated when other species grow in the culture. The risk is far higher for products made from Aphanizomenon flos-aquae (AFA), which is harvested from the wild in Oregon's Upper Klamath Lake.

Oregon set its 1 µg/g limit after a large toxic bloom on the lake in 1996. The World Health Organization's tolerable daily intake is 0.04 µg per kg of body weight, about 2.4 µg for a 60 kg adult. The most contaminated spirulina in the 2017 test would reach that at about 3 g a day, so the margin is thin for a bad batch, and wider for clean ones. The 2023 study used a screening test that can overestimate, and tested only five products.

The FDA's rule for spirulina extract used as a food colour requires it to test negative for microcystin and sets lead, arsenic and mercury limits. That rule covers the colour only. Spirulina supplements have no equivalent federal specification and are not approved by the FDA before sale.

Lead and other quality problems

ConsumerLab reported in 2022 that three of four spirulina supplements it tested had problems: one contained lead and two tablets failed to disintegrate in the expected time. A combination product with spirulina failed for lead in its 2019 tests. A 2013 test of 25 spirulina products found mercury well below limits, so contamination is not universal.

FDA recall records list 13 spirulina-related recalls, mostly blends: Salmonella in greens powders (2014, November 2025 and January 2026), metal fragments, undeclared allergens and two firms making supplements outside good manufacturing practice.

Autoimmune disease and other rare reactions

Spirulina appears to stimulate parts of the immune system, which is where its marketing starts and where a rare risk lies. A 2025 review found five published cases in which dermatomyositis or pemphigus, both autoimmune diseases, began or flared after spirulina. Patients were aged 45 to 82, and most improved after stopping it and taking steroids. In 2004 dermatologists described two pemphigus flares linked to echinacea and spirulina, and a dermatomyositis case after a spirulina and AFA blend.

Memorial Sloan Kettering lists anaphylaxis, a case of muscle breakdown (rhabdomyolysis) in a 28-year-old man after a month of spirulina, and high blood calcium with seizures in a newborn whose mother had taken spirulina for a long time. LiverToxLiverToxA free US National Institutes of Health database that summarises what is known about liver injury caused by medicines, herbs and supplements.More in the glossary says spirulina-related liver injuryDrug-induced liver injuryLiver damage caused by a medicine, herbal product or supplement. It is usually rare and unpredictable, but it can be serious.More in the glossary must be very rare, if it occurs at all.

Who should be careful

• Autoimmune disease or immunosuppressants. Lupus, rheumatoid arthritis, multiple sclerosis, dermatomyositis, pemphigus, or after a transplant: talk to your doctor first.
• Phenylketonuria (PKU). Dried spirulina has about 2.8 g of phenylalanine per 100 g (USDA), so 8 g adds about 220 mg.
• Pregnancy, breastfeeding and children. Health Canada asks pregnant and breastfeeding women to check with a professional, and caps children aged 2 to 4 at 1 g a day.
• Vegans relying on it for B12. Most of its B12 is inactive, and Health Canada does not accept a B12 claim.
• Other medicines. Iron-rich spirulina products should be taken a few hours apart from other medicines, as Health Canada's monograph directs.

How to choose a cleaner product

Buy pure spirulina rather than "blue-green algae" or Klamath blends. Look for a product with published independent testing for microcystins and heavy metals, or a licensed Canadian natural health product, which carries an eight-digit NPN on the label. Powders avoid the tablet problem ConsumerLab found. For another sea-and-pond supplement with a heavy metal question, see sea moss.

How we scored it

Regulatory actions (85), dose safety (80) and interactions (80) are strong: spirulina is legal, licensed in Canada, Class A in USP's review and has few drug interactions. Organ toxicity (72) reflects autoimmune case reports and the liver risk from contaminated batches. Product quality (55) is the weakest factor, with microcystins and lead found in some products and much worse results for algae blends.