Are there side effects of consuming spirulina?

Mike Bohl, MD, MPH, ALM - Contributor Avatar

Written by Linnea Zielinski 

Mike Bohl, MD, MPH, ALM - Contributor Avatar

Written by Linnea Zielinski 

last updated: Jan 08, 2020

3 min read

We’re convinced algae will be the next lobster. Lobster used to be “food for the poor” in 17th and 18th century Europe and North America before rising to its current status as an elite-level eat.

But where lobster has a subtly sweet taste and uncanny camaraderie with butter, types of blue-green algae like spirulina have a long list of health benefits that should propel it to elite status.

Spirulina—a type of cyanobacteria belonging to the blue-green algae family—did have a brief moment in the sun as a “superfood.” Spirulina supplements are made from arthrospira or Arthrospira maxima and Arthrospira platensis, two kinds of microalgae.

Even before that, it was consumed by the ancient Aztecs, who recognized its nutritional power. But after briefly coming back in the 80s as a “superfood” trend, spirulina hasn’t really gotten its due as both a food source of many vital nutrients and a dietary supplement.

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Benefits of spirulina

This blue-green alga is an excellent source of vitamin A, potassium, beta carotene, niacin, riboflavin, and magnesium. It also boasts all of the essential amino acids, making it a “complete” protein. In addition to amino acids, it also includes fatty acids, including heart-healthy omega-3.

This supplement may boost heart health by lowering triglycerides and high cholesterol and reducing high blood pressure. It may also give your immune system a boost, ease seasonal allergy (allergic rhinitis) symptoms, and quell inflammation throughout the body (Mazokopakis, 2014; Selmi, 2011).

It’s believed that many of its health benefits, such as the anti-inflammatory effect of spirulina, are thanks to its antioxidants, the most noteworthy of which is called phycocyanin.

For most people, spirulina consumption is not only beneficial but also convenient. Spirulina tablets are easy to find, and spirulina powder is easy to incorporate into smoothies and drinks. This type of blue-green algae is also a good source of complete protein and omega-3 for vegans.

Possible side effects of spirulina

But despite the wide range of benefits of spirulina, it may not be without some side effects. It’s worth noting that it’s generally well-tolerated, but spirulina is still a supplement, meaning it’s not regulated by the U.S. Food and Drug Administration (FDA).

It’s essential to buy from a high-quality brand you trust. And though it might make a good addition to supplement regimens for most people, there are certain groups like those with specific health conditions for whom it may not be an option for health reasons.

May contain toxins

You’ve probably heard the warnings about mercury in tuna. That’s because anything from the oceans is a product of the water it lives in.

Just as plants soak up nutrients or even pesticides from the soil, so too does spirulina take in what’s in the water around it. If spirulina grows in water containing heavy metals or bacteria, this may be present in the supplements as well.

Certain freshwater blue-green algae also naturally produce microcystins (also called cyanoginosins), a class of toxins. One study found that out of the 18 algae supplements they inspected, 8 contained these toxins at levels above the tolerable daily intake for humans (Roy-Lachapelle, 2017).

In large doses, these toxins may cause liver damage. This underscores the need to only buy supplements from trustworthy brands. Ideally, look for a company that addresses microcystins and their sourcing process openly and clearly. There are ways to grow spirulina to diminish its microcystins content, so look for a brand that follows them (Schmidt, 2014).

May interfere with blood clotting

Blood clotting is necessary, and this process can prevent excessive bruising and bleeding when you’ve been hurt. But spirulina supplements may interfere with or slow down this process.

While this may not be drastic enough to be dangerous for most people, those on blood-thinning medication like warfarin (brand name Coumadin) shouldn’t take these supplements. Other studies have found that spirulina does not affect clotting time, but no research has been conducted on people taking anticoagulants (Jensen, 2015).

For this reason, it’s still necessary to discuss this risk with your healthcare provider and follow their medical advice when it comes to supplements.

Is dangerous for people with phenylketonuria

Phenylketonuria (PKU) is a condition in which people don’t metabolize the amino acid phenylalanine properly.

It’s a rare genetic disorder that’s generally diagnosed at birth. Phenylalanine can build up in the bodies of people with PKU and, left untreated, cause side effects such as seizures and behavioral changes similar to those seen in attention deficit hyperactivity disorder (ADHD) (Stevenson, 2013).

Spirulina (and other algae) contains phenylalanine, so it should be avoided by people with PKU.

It may be an allergen

Yes, some people are allergic to spirulina. One moderately sized study found that people who had another allergy were more likely to have allergic reactions to cyanobacteria, of which spirulina is one.

If you suspect you may be allergic, talk to your healthcare provider who may be able to perform a non-invasive sensitivity test.


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

  • Akao, Y., Ebihara, T., Masuda, H., Saeki, Y., Akazawa, T., Hazeki, K., … Seya, T. (2009). Enhancement of antitumor natural killer cell activation by orally administered Spirulina extract in mice. Cancer Science, 100 (8), 1494–1501. doi: 10.1111/j.1349-7006.2009.01188.x. Retrieved from

  • Cingi, C., Conk-Dalay, M., Cakli, H., & Bal, C. (2008). The effects of spirulina on allergic rhinitis. European Archives of Oto-Rhino-Laryngology, 265 (10), 1219–1223. doi: 10.1007/s00405-008-0642-8. Retrieved from

  • Jensen, G. S., Attridge, V. L., Beaman, J. L., Guthrie, J., Ehmann, A., & Benson, K. F. (2015). Antioxidant and Anti-Inflammatory Properties of an Aqueous Cyanophyta Extract Derived from Arthrospira Platensis: Contribution to Bioactivities by the Non-Phycocyanin Aqueous Fraction. Journal of Medicinal Food, 18 (5), 535–541. doi: 10.1089/jmf.2014.0083. Retrieved from

  • Mazokopakis, E. E., Starakis, I. K., Papadomanolaki, M. G., Mavroeidi, N. G., & Ganotakis, E. S. (2013). The hypolipidaemic effects of Spirulina (Arthrospira platensis) supplementation in a Cretan population: a prospective study. Journal of the Science of Food and Agriculture, 94 (3), 432–437. doi: 10.1002/jsfa.6261. Retrieved from

  • Roy-Lachapelle, A., Solliec, M., Bouchard, M., & Sauvé, S. (2017). Detection of Cyanotoxins in Algae Dietary Supplements. Toxins, 9 (3), 76. doi: 10.3390/toxins9030076. Retrieved from

  • Schmidt, J., Wilhelm, S., & Boyer, G. (2014). The Fate of Microcystins in the Environment and Challenges for Monitoring. Toxins, 6 (12), 3354–3387. doi: 10.3390/toxins6123354. Retrieved from

  • Selmi, C., Leung, P. S., Fischer, L., German, B., Yang, C. Y., Kenny, T. P., et al. (2011). The effects of Spirulina on anemia and immune function in senior citizens. Cellular & Molecular Immunology, 8 (3), 248–254. doi: 10.1038/cmi.2010.76. Retrieved from

  • Stevenson, M., & Mcnaughton, N. (2013). A comparison of phenylketonuria with attention deficit hyperactivity disorder: Do markedly different aetiologies deliver common phenotypes? Brain Research Bulletin, 99, 63–83. doi: 10.1016/j.brainresbull.2013.10.003. Retrieved from

How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

January 08, 2020

Written by

Linnea Zielinski

Fact checked by

Mike Bohl, MD, MPH, ALM

About the medical reviewer

Dr. Mike is a licensed physician and a former Director, Medical Content & Education at Ro.