Who Should Not Take Spirulina
Spirulina has a healthy, natural image, and for most adults a good-quality product is safe. But it is not suitable for everyone. Our editorial team explains which groups should avoid it, why contamination matters and which popular claims do not hold up.
Spirulina in brief
Spirulina is a dried biomass of cyanobacteria, usually Arthrospira platensis or Arthrospira maxima, often loosely called blue-green algae. It is sold as powder, tablets and capsules and is popular in smoothies, plant-based diets and "green" supplement blends.
Its appeal lies in its nutrient profile. By dry weight it is rich in protein and contains iron, B vitamins, carotenoids and the blue pigment phycocyanin. However, the amounts consumed are usually only a few grams a day, so its contribution to the overall diet is modest.
Spirulina is generally regarded as safe for most healthy adults when the product is of good quality. A safety evaluation by the United States Pharmacopeia concluded that it does not pose a serious health risk at typical intakes, while recommending a caution statement for certain groups.
Those groups, and the issue of contamination, are the focus of this article.
Groups who should avoid spirulina
Some people should not take spirulina at all, and others should do so only after professional advice.
| Group | Reason | Recommendation |
|---|---|---|
| People with phenylketonuria (PKU) | Spirulina contains phenylalanine, like other protein sources | Avoid unless approved by the metabolic team |
| People with autoimmune conditions (e.g. lupus, multiple sclerosis, rheumatoid arthritis, autoimmune skin disease) | Possible immune-stimulating effects; case reports of flares | Avoid or discuss with specialist |
| People taking immunosuppressants | Theoretical opposing effect on treatment | Avoid unless doctor agrees |
| Pregnant or breastfeeding women, young children | Insufficient safety data; greater vulnerability to contaminants | Avoid |
| People on anticoagulants or antiplatelet drugs | Limited data on effects on clotting | Seek pharmacist advice |
| People with known allergy to algae or seaweed products | Risk of allergic reaction | Avoid |
Case reports, including those described by Lee and Werth, have linked immune-stimulating supplements containing spirulina to the onset or worsening of autoimmune skin and muscle disease. Case reports cannot prove cause and effect, but they justify a cautious approach.
The contamination problem
The main safety concern with spirulina is not the organism itself but what can accompany it. Spirulina is cultivated in open ponds or tanks, and poor quality control can allow contamination by other cyanobacteria that produce toxins called microcystins.
Microcystins can damage the liver. Studies such as that by Gilroy and colleagues in the United States, and later analyses by Roy-Lachapelle and colleagues, detected microcystins in some blue-green algae supplements, more often in products based on Aphanizomenon flos-aquae than in pure spirulina, but contamination has been reported in both.
Heavy metals such as lead, mercury and arsenic, as well as bacterial contamination, have also been found in some products. Children, pregnant women and people with liver disease are most vulnerable.
- Choose products that state the species clearly.
- Look for evidence of testing for microcystins and heavy metals.
- Prefer established brands that publish certificates of analysis.
- Be cautious with very cheap powders sold online without clear origin.
Common myths about spirulina
Spirulina is often described as a reliable source of vitamin B12 for vegans. In fact, much of the B12-like material in spirulina is pseudovitamin B12, which is inactive in humans. Vegans should rely on fortified foods or a proper B12 supplement.
It is also promoted as a "detox" product. There is no robust evidence that spirulina removes toxins from the body in healthy people; the liver and kidneys perform this function.
Claims about weight loss, cholesterol and blood sugar are based on small studies with inconsistent results. A review by Karkos and colleagues described promising but preliminary findings that require larger, better-designed trials.
Finally, spirulina is sometimes presented as a complete protein replacement. At typical doses of a few grams, it adds only a small amount of protein compared with ordinary foods.
Side effects and when to stop
Even in suitable users, spirulina can cause mild side effects such as bloating, nausea, diarrhoea, headache or an unpleasant taste. Starting with a small amount helps assess tolerance.
Stop taking it and contact a doctor if you develop yellowing of the skin or eyes, dark urine, abdominal pain, rash, muscle weakness or joint pain, especially if you have an autoimmune condition.
Tell your GP and pharmacist about any supplement you use, including "natural" ones, as this helps them interpret test results and avoid interactions.
In the UK, spirulina is sold as a food supplement and is not licensed as a medicine, so manufacturers cannot claim it treats or prevents disease.
Editorial conclusions
Spirulina is safe for most healthy adults when it comes from a reputable, tested source. It should be avoided by people with phenylketonuria, autoimmune conditions or those on immunosuppressants, and by pregnant or breastfeeding women and young children.
Contamination with microcystins and heavy metals is the main practical risk, so product quality matters more than the dose.
It is not a reliable source of vitamin B12 and not a detox remedy.
You may also like our articles on chlorella versus spirulina, vitamin B12 on a vegan diet, and how to check supplement quality.
References
- Marles RJ, Barrett ML, Barnes J, et al. United States Pharmacopeia safety evaluation of spirulina. Crit Rev Food Sci Nutr. 2011;51(7):593–604.
- Gilroy DJ, Kauffman KW, Hall RA, Huang X, Chu FS. Assessing potential health risks from microcystin toxins in blue-green algae dietary supplements. Environ Health Perspect. 2000;108(5):435–439.
- Roy-Lachapelle A, Solliec M, Bouchard MF, Sauvé S. Detection of cyanotoxins in algae dietary supplements. Toxins (Basel). 2017;9(3):76.
- Lee AN, Werth VP. Activation of autoimmunity following use of immunostimulatory herbal supplements. Arch Dermatol. 2004;140(6):723–727.
- Karkos PD, Leong SC, Karkos CD, Sivaji N, Assimakopoulos DA. Spirulina in clinical practice: evidence-based human applications. Evid Based Complement Alternat Med. 2011;2011:531053.
