Spirulina is a popular supplement and ingredient made from blue-green algae.
Although it has several benefits, you may wonder if it has any side effects.
This article reviews the potential downsides and side effects of spirulina.
What is spirulina?
Spirulina is a blue-green algae commonly used as a dietary supplement. It may provide antioxidant, anti-inflammatory, and immune-boosting benefits.
Side effects and downsides
Here are some of the potential side effects and downsides of spirulina.
May be contaminated with toxins
Spirulina harvested in the wild poses a significant risk of contamination. The algae may harbor toxins if it grows in a body of water that’s polluted with heavy metals, bacteria, or harmful particles called microcystins (2).
In fact, microcystins are produced by blue-green algae as a defense mechanism against predators. When consumed in high amounts, they’re toxic to your liver (
May worsen autoimmune conditions
Because spirulina boosts your immune system, it may worsen certain autoimmune diseases — such as lupus, multiple sclerosis, and rheumatoid arthritis — in which your immune system attacks your body (2).
Spirulina bolsters your immune system by strengthening immune cells called natural killer (NK) cells, which attack perceived threats on a cellular level (
However, by strengthening the NK cells in people with autoimmune conditions, this algae may exacerbate these conditions.
If you have an autoimmune condition, you should avoid spirulina and other algae supplements (2).
May slow blood clotting
Clotting helps prevent excessive bleeding or bruising when you’re injured (
For those taking blood thinners or who have bleeding disorders, spirulina may be dangerous because it could lessen your blood’s ability to clot, causing more bruising and bleeding (2).
Thus, you should avoid spirulina if you have a bleeding disorder or are on blood thinners.
Some people may be allergic to spirulina. In severe cases, reactions can be fatal (
According to one study, people with other allergies are more likely to react negatively to spirulina than those without other allergies. To be safe, those with allergies should avoid this supplement or consult their healthcare provider before using it (
Spirulina and other algae also contain phenylalanine, a compound that people with phenylketonuria (PKU) — a rare inherited condition — should strictly avoid (2).
Spirulina may be contaminated with harmful compounds, thin your blood, and worsen autoimmune conditions. Some people may be allergic, and those with PKU should avoid it.
How to avoid side effects
As spirulina may have some drawbacks, especially in certain populations, it’s best to consult your healthcare provider before taking it.
To avoid spirulina that has been contaminated with microcystins or toxins, only purchase products from trusted brands that have been tested by third-party organizations, such as U.S. Pharmacopeia (USP), ConsumerLab, or NSF International.
Keep in mind that even certified products may not be completely free of contaminants, as dietary supplements are largely unregulated in the United States.
Purchasing from trusted brands can reduce your risk of contamination. However, there’s no guarantee that spirulina products are 100% contaminant-free.
The bottom line
Although widely considered safe, spirulina has several potential side effects.
Some supplements may be contaminated by toxins. What’s more, this algae may worsen some autoimmune conditions and thin your blood.
You should avoid spirulina if you take blood thinners or have an autoimmune condition, bleeding disorder, allergies, or PKU.
If you’re unsure whether this supplement is right for you, consult your medical practitioner.