Spirulina Side Effects

Oftentimes, consumers may be under the impression that all nutrition supplements are always considered safe for everyone just because they are considered natural. Is that the case with spirulina? Keep reading to find out if spirulina has any side effects, and if certain populations of people should avoid spirulina in their diet.

Key Takeaways

  • Spirulina has become popular for its impressive nutritional profile and proposed health benefits researched in the literature
  • There are some groups of people that should avoid spirulina due to side effects, though it’s generally safe for most people
  • Purchasing from a reputable, third party tested supplier is one of the best ways to help prevent side effects of spirulina

What Is Spirulina?

Spirulina is a blue-green algae that is commonly known as a “superfood” for its impressive nutritional profile. One tablespoon contains 4 grams of protein, it is a good source of some B vitamins, and it also contains iron.

It has been studied for its antioxidant and anti-inflammatory properties. Some proposed health benefits of spirulina include improved cholesterol, blood lipid profile, triglycerides, reduced seasonal allergy symptoms, and possibly anti-cancer properties.

But are there any side effects for this seemingly perfect “superfood?”

Green smoothie with spirulina

Who Should Not Take Spirulina?

Although spirulina is safe for most people, there are a few groups of people based on certain medical conditions or medications that should avoid spirulina.


Those who are pregnant and breastfeeding should avoid taking spirulina. While spirulina is nutrient dense and has been studied for its antioxidant potential, there is not enough evidence that spirulina is safe for both mom and baby during pregnancy.


Phenylketonuria, also known as PKU, is a rare inherited disorder of protein metabolism in which those with this condition cannot break down the amino acid phenylalanine.

People who have PKU need to avoid phenylalanine and have a lower protein diet and avoid artificial sweeteners like aspartame.

Spirulina contains phenylalanine and should be avoided if you have PKU.


Those on immunosuppressant medications, anti-diabetic medications, and blood thinners should avoid spirulina or other blue-green algaes or speak with your doctor before starting it as they may interact with these kinds of medications, making them work differently or not as effective.

Autoimmune Conditions

Evidence suggests that spirulina has an effect on inflammatory markers. Some autoimmune conditions like lupus and rheumatoid arthritis cause the immune system to already be on high alert.

Taking spirulina could possibly worsen symptoms of autoimmune conditions and this and other blue-green algaes should be avoided.

Man drawing side effects on glass

Are There Side Effects Of Spirulina?

Most studies using spirulina indicate that it is safe for most people and that side effects are not common.

Currently, there is no established dose for spirulina. The current research suggests a wide range of 1-8 grams per day has shown beneficial effects with minimal side effects.

High doses may cause stomach upset, nausea, diarrhea, or headaches. More research is needed on long-term studies with spirulina and doses higher than 8 grams daily.

Another important aspect is that spirulina harvested from the wild in lakes, oceans, or ponds could be at an increased risk of developing a toxin called microcystins.

Microcystins are actually a defense mechanism that spirulina has in place when faced with something harmful, such as polluted waters or bacteria.

Unfortunately, microcystins harm human health and could cause liver injury if any blue-green algae are consumed that has been contaminated with bacteria or polluted waters.

Most spirulina for consumption is now grown in a controlled environment like farms or greenhouses. The risk of spirulina being contaminated with microcystins is much lower since it is not harvested from the wild.

Is There A Risk Of Heavy Metal Toxicity?

Heavy metals are metals that have a high density, and some of them could be toxic to our health at high levels.

Some heavy metals linked with certain side effects or medical conditions at high levels are lead, cadmium, mercury, and arsenic.

One review tested 27 spirulina products and found all of them were significantly lower than the recommended daily limit of mercury, showing that they were safe to consume.

If water or soil is contaminated with these heavy metals, it can leak into our food or supplements.

So, there is a risk that spirulina could be contaminated with heavy metals, which is why purchasing spirulina and all nutrition supplements from a reputable supplier is important.

Can You Be Allergic To Spirulina?

There is a possibility you could be allergic to spirulina.

First, it could be a true allergy to spirulina, just like someone allergic to peanuts.

Additionally, if you are allergic to fish, shellfish, or any other foods from the ocean, it would be advised to avoid spirulina due to the risk of allergic reactions.

Does Spirulina Make You Poop?

There is currently conflicting evidence around if spirulina causes gas or more frequent bowel movements or constipation.

Starting a new supplement like a greens powder for the first time over the first few days may increase digestive irritation but it is usually temporary.

If you experience any unwanted or uncomfortable side effects from spirulina, remove it from your diet and inform your doctor.

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How Can You SAFELY Incorporate Spirulina Into Your diet?

Spirulina can be safely incorporated into your diet by choosing a reputable, third-party-tested brand.

Two third-party testing logos to look out for on bottles are United States Pharmacopeia (USP) certifications and National Sanitation Foundation (NSF) Certified for Sport certifications. The NSF also tests food, water, consumer products, and some nutrition supplements.

Spirulina comes in tablet form, or powder form, or it is also often seen in a greens blend in green powders.

Another way to safely take spirulina is to follow the directions as it reads on the bottle. Taking too much, or starting at too high a dose, can help prevent unwanted side effects.

Green powders can support a healthy diet, not replace one, by providing vitamins, minerals, and green vegetables. They also often contain adaptogens to support the stress response and improve sleep, and also sometimes contain probiotics and prebiotics. 

Supergreen Tonik has 2000mg of organic spirulina, or 2 grams, which is within the researched dose discussed above.

The spirulina is in Supergreen Toniks’ green blend, which also has organic collards powder, organic spinach leaf powder, and more.

They let you know how much of each ingredient is in their product, so no proprietary blends or confused consumers wonder what doses their green powder includes. 

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Final Thoughts

Spirulina is generally safe for most people, though there are some side effects or possible risks with taking too high doses or consuming spirulina from a non-regulated environment.

More research is needed on long-term studies using spirulina to assess the side effects. 

Like always, the safest way to incorporate any new nutrition supplement like spirulina or green powder into your diet is to speak with your own doctor or dietitian first. They can help guide you on what may or may not be appropriate to take based on your medical history.

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