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What is Spirulina? + Nutrition, Side Effects & Dosage

Written by Carlos Tello, PhD (Molecular Biology) | Last updated:
Puya Yazdi
Medically reviewed by
Puya Yazdi, MD | Written by Carlos Tello, PhD (Molecular Biology) | Last updated:

Once declared the “best food for the future” by the World Health Organization, this blue-green algae is a protein-rich antioxidant that may support and maintain your immune system. Read on to learn more about spirulina.

What Is Spirulina?

Spirulina is a dried supplement made from two species of blue-green algae, Arthrospira platensis and Arthrospira maxima. The Kanembu tribe in Chad call it dihé; the Aztecs who lived in the valley of Mexico called it tecuitlatl [1, 2, 3, 4].

The algae naturally grows in warm freshwater lakes like Lake Texcoco in Mexico and Lake Chad, which sits on the border of Chad, Niger, Nigeria, and Cameroon. Locals traditionally harvest the algae and dry it in “cakes” [4].

Once it’s been dried, spirulina contains up to 70% protein, is a nutrient-rich antioxidant, and takes less land, water, and energy to produce than staple crops like corn and soy. Farmers use it to enrich their animal feeds and improve the quality of meat they produce. It pulls huge quantities of carbon dioxide out of the atmosphere, and it may even be used to convert city sewage back to clean water [1, 5].

Spirulina gathered attention as a possible pharmaceutical in the 1940s and 50s. In 1974, the World Health Organization declared it the “best food for the future” to combat malnutrition, especially in children [4].

Spirulina is a dried blue-green algae that contains 70% protein once dried. It is considered an important “food for the future” by the WHO.



The most significant bioactive compounds in spirulina are the phycocyanins, including C-phycocyanin. This is a powerful antioxidant and anti-inflammatory molecule with a surprising cascade of effects: it has been found to protect brain and liver cells [1, 6].

C-phycocyanin has a very similar structure to the human blood protein bilirubin, which is a product of the breakdown of old red blood cells. Bilirubin happens to be a natural antioxidant: it binds to oxygen free radicals to form biliverdin. Elevated bilirubin can signal an underlying health problem, but in most people, bilirubin is protective. People with low levels of bilirubin are more likely to suffer from atherosclerosis and heart disease. C-phycocyanin may help restore the oxidative balance in people with low bilirubin [7, 8, 9, 10, 11].

Spirulina is rich in phycocyanins, which are similar in structure to human bilirubin, a natural antioxidant.

Other Functional Compounds

Spirulina boasts a range of bioactive compounds like phenols, flavonoids, and polysaccharides. The phenols and flavonoids contribute to this algae’s antioxidant and anti-inflammatory properties; the polysaccharides boost the immune response [1].

Important Nutrients

Dried spirulina is very high in a wide variety of nutrients. 100 g (or about 3.5 oz) of dried spirulina contains more than 100% of the recommended daily intake of total proteins, vitamin B1 (thiamin), vitamin B2 (riboflavin), iron, and copper. It is also a significant source of vitamin E, vitamin K, vitamin B3 (niacin), folate, magnesium, potassium, and manganese [1, 12, 13, 14, 15, 16, 17].

Note that if you are taking a few grams of spirulina as a supplement, these nutrients will probably not be present in high enough quantities to make a real difference in your nutrient status.

Spirulina is Not a Source of Vitamin B12

Spirulina contains inactive compounds called corrinoids, one of which has a structure very similar to vitamin B12. In fact, this corrinoid, which is sometimes called pseudovitamin B12, is so similar to the real thing that researchers cannot tell the difference with conventional lab tests. As a result, some nutrition sources report that spirulina contains large quantities of B12 even though the pseudovitamin corrinoid has no biological activity and cannot be substituted for vitamin B12 [18, 19].

People who eat a vegetarian diet may have difficulty finding plant-based foods containing vitamin B12. This essential vitamin supports the nervous system and bone marrow, and a deficiency can cause low blood cell count or neurological problems [20].

If you are a vegetarian, do not rely on spirulina for vitamin B12. It contains an inactive corrinoid, not the real vitamin.

Spirulina is rich in many nutrients, but it is not a source of vitamin B12.

How Does Spirulina Work?

Antioxidant Activity

Spirulina is a powerful antioxidant. It contains multiple active compounds with antioxidant properties, including phycocyanins, phenols, and flavonoids [1].

Thiobarbituric acid reactive substances, or TBARS, are byproducts of oxidative stress: when reactive free radicals damage tissues, TBARS are released; this makes them useful for measuring oxidative stress. In multiple cell studies, spirulina dramatically decreased the production of TBARS, even when the cells were also exposed to the toxic chemotherapy drug fluorouracil [21].

Innate antioxidant enzymes – such as glutathione peroxidase (GPX), selenium-dependent glutathione peroxidase (GPX-Se), and oxidized glutathione reductase (GR) – defend the body from oxidative stress by converting free radicals into their harmless forms. In a cell study, spirulina protected these enzymes in the presence of high levels of iron [21, 22].

C-phycocyanin is very similar to bilirubin, an antioxidant that forms when red blood cells are broken down. It may block NADPH oxidase, which produces free radicals under stress [7, 23].

Spirulina is a source of many antioxidant compounds that reduce the production of TBARS and protect the action of glutathione peroxidase in cell studies.

Anti-Inflammatory Activity

Tumor necrosis factor (TNF) and interleukin 6 (IL-6) are inflammatory molecules called cytokines. Cyclooxygenase-2 (COX-2) is an enzyme that produces inflammatory compounds. Prostaglandin E2 (PGE2) is a hormone that, among other functions, increases inflammation. In animal models of age-related inflammation, spirulina decreases TNF and IL-6, suppresses COX-2, and reduces PGE2 expression [24].

In rats, spirulina prevented mast cells from releasing histamine, a powerful inflammatory compound [25].

Note that some studies suggest spirulina may increase certain inflammatory cytokines, such as IL-1 from macrophages, as part of its immune-boosting activity. Added together, however, spirulina’s total effect is a decrease in inflammation [26].

In animal models, spirulina decreases markers of inflammation like TNF, IL-6, COX-2, and PGE2.

Strengthening the Immune System

In animals, spirulina activates multiple branches of the immune system. In mouse studies, polysaccharides from spirulina increased activity in the bone marrow, thymus, and spleen: these structures grow and develop blood cells, and their health is vital to a strong immune system. The reason for this may be that spirulina increases expression of bcl-2, a gene that prevents cells from dying, specifically in these tissues [26].

Phycocyanin from spirulina may boost the activity of erythropoietin, a hormone that increases red blood cells. Though we know them as the oxygen-carrying workhorses of the blood, red blood cells also participate in the immune response: proteins inside them are toxic to bacteria and yeast, and these cells can act as “decoys” for invading viruses. The viruses attack red blood cells instead of other tissues, leaving them vulnerable to white blood cells [26, 27].

C-phycocyanin and spirulina polysaccharides may also increase the production of white blood cells, the most important cells for immunity. In animal studies, spirulina increased the number and activity of macrophages, a type of white blood cell that “eats” bacteria, viruses, and even cancer cells [26, 28, 1, 29].

In cells and animals, spirulina also increased the activity of natural killer cells, which attack viruses and tumors. In multiple studies, animals given spirulina also had increased lymphocyte activity and antibody production [26, 28, 1, 29].

Spirulina may improve the function of immune cells and organs by protecting them from toxins, damage, and environmental stress. In this way, the antioxidant and immune-boosting properties of spirulina may be linked [26].

In short, spirulina triggers a series of changes to the immune and inflammatory responses, possibly reducing overall inflammation while strengthening immunity [26, 1].

Certain active compounds in spirulina have activated the immune system of experimental animals and increased the activity of immune cells like natural killer cells.

Other Mechanisms

Spirulina may have other mechanisms of action which are currently under investigation.

For example, spirulina may prevent harmful mutations in p53, an important gene for preventing tumor growth. And unlike the lipopolysaccharides from bacteria, the ones in spirulina may activate a pathway that decreases certain autoimmune cytokines (IL-17) and increases cancer-fighting ones (IFN-γ) [30, 31].

In multiple cell studies, spirulina prevented a variety of viruses (including HIV) from dividing. Many of these effects have not been investigated in animals or humans; however, in one study, spirulina significantly increased the survival rate of hamsters infected with a deadly herpes virus [26].

For more about the potential benefits of spirulina supplementation, check out this post.

Side Effects & Safety

This list does not cover all possible side effects. Contact your doctor or pharmacist if you notice any other side effects.

Call your doctor for medical advice about side effects. In the US, you may report side effects to the FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch. In Canada, you may report side effects to Health Canada at 1-866-234-2345.

Spirulina is considered very safe. It was a common food for the Aztecs and in parts of Chad, and it can be consumed in large quantities with few expected side effects. People taking spirulina have rarely reported insomnia and stomach upset; these side effects may or may not have been caused by spirulina [32, 1].

Other rare health problems have been reported in people taking spirulina. These effects include autoimmune skin damage, liver toxicity, and anaphylactic shock. Most people who suffered serious side effects after taking spirulina were also taking another medication for a serious health condition; spirulina may, therefore, interact with some drugs and diseases. If you are taking medication – especially for autoimmune disease, blood pressure, or cholesterol – talk to your doctor before supplementing with spirulina [1].

These side effects could have also been due to supplement contamination.

Spirulina is considered very safe, and some people eat large quantities as food. However, rare side effects like skin damage, liver toxicity, and anaphylactic shock have been reported. It may also interact with some medications.

Allergic Reaction

Some people may suffer an allergic reaction to spirulina. At least two cases have been reported, and in both, the allergy was severe. This reaction is extremely rare, but if you are concerned, you can ask your doctor to check for spirulina allergy [1].


The most significant safety risk for people taking spirulina comes from what else might sneak into the Arthrospira biomass. Some farmed spirulina grows in sealed tanks called bioreactors, but most spirulina is farmed in outdoor ponds, where it is difficult to prevent other bacteria from growing alongside Arthrospira. Some of these other bacteria are human pathogens, and others can produce dangerous toxins that persist in the final product. Choose a high-quality spirulina supplement to avoid these risks [2].


Spirulina is very high in the amino acid phenylalanine, containing between 2.6 and 4.1 g of phenylalanine per 100 g of dried spirulina. For most people, this is a good thing: phenylalanine is required for tissue growth and repair. However, for people with phenylketonuria, or PKU, this can make spirulina dangerous to consume [1, 33].

People with PKU don’t have enough of the enzyme phenylalanine hydroxylase, which normally converts phenylalanine into another amino acid, tyrosine. PKU can be managed through careful diet and supplementation with an amino acid blend. Since spirulina is very high in phenylalanine, people with PKU should completely avoid spirulina [33, 1].

Autoimmune Activation

Spirulina has enough immune-boosting power that it may activate or worsen an autoimmune disorder in people who are prone to such conditions. If you have an autoimmune disorder or if autoimmunity runs in your family, talk to your doctor before supplementing [34, 26].

Some people may have a rare allergic reaction to spirulina. People with phenylketonuria or autoimmune diseases should consult their doctors before consuming spirulina. Another concern is the potential for contamination with other bacteria, including human pathogens.

Drug Interactions

Supplement/Herb/Nutrient-drug interactions can be dangerous and, in rare cases, even life-threatening. Always consult your doctor before supplementing and let them know about all drugs and supplements you are using or considering.

Spirulina probably should not be combined with immunosuppressive drugs or any medication that is metabolized by CYP450 enzymes.


Because spirulina boosts immunity, it may interfere with the effects of drugs that suppress the immune response. Immunosuppressants are usually given after a transplant or graft in order to prevent the body from rejecting its new organ or tissue. They are also used to manage autoimmune disorders like multiple sclerosis, arthritis, and lupus [35, 36, 37].

Immunosuppressive drugs include glucocorticoids like prednisone, cytostatics like azathioprine, drugs that act on immunophilins like cyclosporine, and some other drugs like opioids [36, 38, 39, 40].

If you are taking any medication to suppress the immune response, we recommend talking to your doctor before supplementing with spirulina.

CYP Substrates

In rats, spirulina supplements increased and decreased the levels of certain cytochrome P450 (CYP) enzymes. These enzymes break down many drugs and other compounds; spirulina may, therefore, interact with medications that rely on CYP enzymes to break them down and remove them from the body [41, 42, 43].

In rats, spirulina decreased:

  • CYP1A2 activity: This enzyme breaks down a variety of medications, including many antidepressants, some antipsychotics, some painkillers, caffeine, ropivacaine, zolmitriptan, tamoxifen, cyclobenzaprine, propranolol, and warfarin [44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55].
  • CYP2E1 activity: This enzyme breaks down a variety of medications, including anesthetics, acetaminophen (Tylenol), nicotine, ethanol, industrial toxins like benzene, theophylline, chlorzoxazone, and zopiclone [41, 44, 56, 57, 58].

Spirulina also decreased the activity of some other less-known CYP enzymes in rats. But due to the lack of additional research, we do not currently have a complete list of medications that may interact with spirulina [59].

Talk to your doctor before combining spirulina with medication.

In rats, spirulina modified the activity of several CYP enzymes, meaning that it may have the potential to increase or decrease the effects of some medications.



People with PKU must have two abnormal alleles for defective phenylalanine hydroxylase at the PAH gene. Any two abnormal alleles can cause the disease, even if the two mutations are at different SNPs. Dozens of different SNP variants can be responsible for PKU; the most common is Arg408Trp, or the T allele at rs5030858 [33, 60].

CYP Genes

Variants in the CYP enzymes mentioned above may change how your body responds to spirulina. Spirulina increases certain CYP enzymes and decreases others. In rats, it decreases the expression of CYP1A2 and CYP2E1. People who already have decreased activity in these enzymes may wish to avoid spirulina, especially if they are taking certain prescription medications [41].

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Further Reading


Spirulina is the dried product of two species of cyanobacteria, or blue-green algae. It has been a staple food for people living around Lakes Texcoco and Chad for centuries; the health effects of its active phycocyanins, phenols, and polysaccharides more recently made it a popular supplement.

Low-quality spirulina supplements may be contaminated with harmful bacteria or toxins. Very rarely, people have had serious allergic reactions to spirulina; it has also activated or worsened autoimmunity in sensitive people. People with phenylketonuria or anyone taking immunosuppressive or CYP-metabolized drugs should avoid spirulina.

About the Author

Carlos Tello

Carlos Tello

PhD (Molecular Biology)
Carlos received his PhD and MS from the Universidad de Sevilla.
Carlos spent 9 years in the laboratory investigating mineral transport in plants. He then started working as a freelancer, mainly in science writing, editing, and consulting. Carlos is passionate about learning the mechanisms behind biological processes and communicating science to both academic and non-academic audiences. He strongly believes that scientific literacy is crucial to maintain a healthy lifestyle and avoid falling for scams.


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