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Spirulina Supplements: Side Effects and Safety Concerns

Spirulina is a blue-green algae that was already eaten by the Mayas, Toltecs and Kanembu in Mexico during the Aztec civilization. Today, spirulina is often marketed as a superfood due to its high concentration of nutrients. But are spirulina supplements really safe for consumption? Are there any potential side effects or adverse reactions you should be concerned about

According to a research paper published in the August 2010 issue of Cardiovascular Therapy, uncontaminated spirulina is generally considered safe for human consumption supported by its long history of use as a food, and its favorable safety profile in animal studies. However, the researchers point out that rare cases of side effects have been reported, and additional clinical studies are warranted to systemically establish the safety profile of spirulina in humans. What's more, given the lack of regulatory standards on the production of dietary supplements in the U.S., there have been some concerns about low quality spirulina products that may have been contaminated with heavy metals and microcystins.

Animal Study Finds No Side Effects

A study published in Food Science and Technology Research investigated the effects of spirulina supplementation both in the short term (7 days) and in the long term (12 weeks). In the short-term experiment, no signs of toxicity were observed after feeding mice with high doses of spirulina (30 and 10 g/kg body weight of fresh and dried Spirulina platensis, respectively). The long-term experiment consisted of two sub-experiments: In each experiment, four groups of male and female rats were given fresh or dried spirulina daily at various doses. In all instances, the consumption of spirulina showed no effect on behavior, food and water intake, growth or health status of the experimental animals during the twelve-week study. In addition, post-mortem examination found no abnormalities in the gross findings.

Concerns About Contamination with Heavy Metals and Microcystins

Mercury and other toxic heavy metals heavy been found in some supplements derived from spirulina that has been grown in uncontrolled open water sources. Consumption of such spirulina supplements could lead to accumulation of heavy metals in the body, which could have toxic effects. What's more, some spirulina supplements have been found to contain microcystins which are toxic to the liver and probable tumor promoters. While these toxic compounds are not produced by spirulina itself, they may occur in spirulina powder and tablets as a result of contamination with microcystin-producing blue-green algae such as Microcystis aeruginosa. While the U.S. National Institutes of Health describe uncontaminated blue-green algae as "possibly safe" for most adults, they also state that contaminated blue-green algae could cause liver damage, stomach pain, vomiting, nausea, weakness, thirst, rapid heartbeat, shock and – in the worst case – even death.

Spirulina Side Effects

As the U.S. Food and Drug Administration does not impose strict regulations on the production of supplements such as spirulina tablets, it is best to purchase spirulina products only from trusted distributors to reduce your risk of getting a batch of contaminated spirulina. If you are interested in buying US-grown spirulina that has been tested for heavy metals and microcystins, check out Nutrex Hawaii's spirulina tablets and powders which are available on Amazon.com, Amazon.co.uk and Amazon.ca. Nutrex Hawaii's spirulina is cultivated in a biosecure zone that is certified free of pesticides, herbicides and industrial pollutants, and according to the company's website, each lot of Nutrex Hawaii spirulina goes through a series of over 15 different tests that check the algae for, among other things, heavy metals and microbes. Their spirulina is also periodically tested for microcystins, and as of the writing of this article (June 2015), has never been found to be contaminated with these harmful compounds.

Who Should Avoid Taking Spirulina Supplements?

Everyone (especially children) should avoid spirulina supplements that may have been contaminated with microcystins or heavy metals such as mercury, but certain groups of people might also want skip spirulina products altogether. The U.S. National Institutes of Health states on their website that people with auto-immune diseases, such as multiple sclerosis (MS), lupus, rheumatoid arthritis (RA) and pemphigus vulgaris, would be better off avoiding spirulina because the blue-green algae may make the immune system more active, which in turn may worsen the symptoms of auto-immune diseases.

They also point out that spirulina contains phenylalanine, an amino acid that may make phenylketonuria worse, so people with phenylketonuria should also avoid taking spirulina supplements. Phenylketonuria is a rare inherited disorder that causes phenylalanine to build up in the body.

Spirulina may also cause side effects or adverse reactions if taken together with certain medications, or it may affect the effectiveness of the medication. Therefore, if you are taking any medications or herbal supplements, talk to a qualified health care professional before adding spirulina to your diet. Medications and supplements that are particularly likely to interact with spirulina include immunodepressants and anticoagulant/antiplatelet drugs.

Finally, the U.S. National Institutes of Health recommends that pregnant or breast-feeding women avoid spirulina until more is known about the effects of spirulina in pregnant and breast-feeding women and their (unborn) babies (see also Is Spirulina Safe During Pregnancy?).


1. O. Ciferri and O. Tiboni. The biochemistry and industrial potential of Spirulina. Ann Rev Microbiol, 1985;39:503-526.
2. D. Deng and T. Chow (2010). Hypolipidemic, Antioxidant and Antiinflammatory Activities of Microalgae Spirulina. Cardiovasc Ther., 28(4): e33-e45.
3. N. Hutadilok-Towatana et al (2008). A Subchronic Toxicity Study of Spirulina platensis. Food Sci and Technol Res., 14:351.
4. Johnson PE, Shubert LE (1986). Accumulation of mercury and other elements by Spirulina (cyanophyceae) Nutr Rep Int., 34:1063-1070.
5. Blue-green algae. MedlinePlus, National Institutes of Health, Retrieved June 16, 2015.
6. D J Gilroy et al (2000). Assessing potential health risks from microcystin toxins in blue-green algae dietary supplements. Environ Health Perspect, 108(5): 435-439.

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