What are the side effects of taking spirulina?

November 17, 2025 •

3 min read

While often hailed as a 'superfood,' some individuals experience adverse reactions after consuming spirulina. This blue-green algae can, in rare cases, trigger side effects ranging from mild gastrointestinal issues to more serious complications, especially in contaminated products or those with specific health conditions.

Quick Summary

Potential risks of spirulina include gastrointestinal issues, autoimmune flare-ups, and interaction with medications. Contamination with toxins or heavy metals is a significant safety concern, particularly with unregulated products.

Key Points

Gastrointestinal Distress: Mild issues like bloating, gas, and diarrhea are among the most commonly reported side effects, especially when first starting spirulina.
Contamination Risk: Poorly regulated spirulina products can be contaminated with harmful toxins like microcystins and heavy metals, posing serious health risks including liver damage.
Autoimmune Conditions: Due to its immune-boosting effects, spirulina can worsen symptoms or trigger flare-ups in individuals with autoimmune diseases such as lupus or rheumatoid arthritis.
Blood Clotting Interference: Spirulina's anticoagulant properties can be dangerous for people with bleeding disorders or those on blood-thinning medications.
Uric Acid Build-up: High doses of spirulina can increase uric acid levels, which is a concern for individuals with a history of gout or kidney stones.
Phenylketonuria (PKU): People with this rare metabolic disorder must avoid spirulina as it contains phenylalanine, an amino acid they cannot process.
Importance of Purity: Only purchase spirulina from reputable brands with third-party testing to ensure it is free from contaminants and safe for consumption.

Common and Mild Side Effects of Spirulina

For most healthy individuals, spirulina is well-tolerated when taken in recommended doses, but some people may experience mild and temporary side effects. These symptoms often occur as the body adjusts to the supplement and typically resolve on their own.

Gastrointestinal Upset: Some of the most frequently reported side effects involve the digestive system. These can include:
- Bloating
- Gas
- Diarrhea or abdominal cramps
- Nausea
Headaches and Dizziness: A smaller number of users report experiencing headaches or a feeling of dizziness after taking spirulina.
Skin Irritation: Skin-related reactions like itching or rashes are also possible, though less common.

Potential for Contamination

One of the most significant risks associated with spirulina supplements comes from the potential for contamination. Because spirulina is often cultivated in open ponds, it can easily absorb heavy metals and other toxins from its environment.

Heavy Metals: Spirulina can accumulate heavy metals like mercury, lead, and arsenic if grown in polluted water. Independent testing and certifications are crucial for ensuring a product is safe.
Microcystins: Harmful blue-green algae that produce microcystin toxins can contaminate spirulina batches. These toxins are highly dangerous to the liver and can cause severe illness or even death in extreme cases. Choosing products from certified controlled environments significantly reduces this risk.

Serious Health Risks and Contraindications

While rare, certain pre-existing conditions can increase the risk of serious complications from spirulina consumption. It's crucial for some individuals to avoid this supplement entirely.

Autoimmune Diseases: Since spirulina can boost immune system activity, it may exacerbate autoimmune conditions where the body's immune system mistakenly attacks its own cells. Those with conditions like lupus, multiple sclerosis, or rheumatoid arthritis should avoid spirulina. Clinical studies have shown spirulina may trigger or worsen flare-ups in susceptible individuals, such as those with dermatomyositis.
Bleeding Disorders: Spirulina has anticoagulant properties, which means it can slow down blood clotting. People with bleeding disorders or those taking blood-thinning medications should avoid it due to an increased risk of bruising and bleeding.
Phenylketonuria (PKU): This is a rare genetic disorder where the body cannot properly metabolize the amino acid phenylalanine. Spirulina contains this amino acid, making it dangerous for people with PKU.
Liver and Kidney Issues: Contaminated spirulina containing microcystins can cause liver damage. Additionally, due to its high nucleic acid content, excessive spirulina intake can increase uric acid levels, potentially contributing to gout or kidney stones in susceptible individuals.

Comparison of Spirulina Side Effects


Side Effect Category	Common Severity	Frequency of Occurrence	Population Most at Risk
Gastrointestinal Discomfort	Mild	Relatively Common	Sensitive individuals, new users
Headaches & Dizziness	Mild	Uncommon	Anyone, usually resolves over time
Contamination (Toxins/Metals)	Potentially Severe	Dependent on product quality	All consumers, especially with unregulated products
Autoimmune Flare-ups	Potentially Severe	Rare	Individuals with pre-existing autoimmune conditions
Bleeding Complications	Potentially Severe	Rare	Those with bleeding disorders or on blood thinners
PKU Complications	Severe	Extremely Rare	Individuals with phenylketonuria
Liver/Kidney Issues	Severe	Rare	Individuals with pre-existing organ issues; due to contamination/excessive intake

The Role of Quality and Regulation

Since dietary supplements are not strictly regulated by the FDA, the quality of spirulina products can vary dramatically. This makes purchasing from reputable brands that provide third-party testing for contaminants, like heavy metals and microcystins, critically important. Products grown in controlled, closed systems are generally safer than those cultivated in open ponds.

Conclusion

While the nutritional benefits of high-quality spirulina are significant, understanding the potential side effects of taking spirulina is essential for safe consumption. For the majority of healthy individuals, these effects are mild and temporary. However, certain populations, such as those with autoimmune diseases or PKU, must avoid it entirely. The risk of contamination with heavy metals and microcystins underscores the critical need to source products from trusted, third-party-certified brands. As with any supplement, consulting a healthcare provider is recommended, especially for those with underlying health concerns or on medication.

For further information on supplement safety, consult reliable health resources like the National Institutes of Health.

Frequently Asked Questions

Individuals with autoimmune diseases like lupus, multiple sclerosis, or rheumatoid arthritis should avoid spirulina. People with the genetic disorder phenylketonuria (PKU), bleeding disorders, or those taking blood-thinning medication should also refrain from taking it.

Yes, some people may experience mild gastrointestinal issues, including bloating, gas, diarrhea, or nausea, particularly when they first start taking spirulina or if they have a sensitive stomach.

Contaminated spirulina can contain microcystins and heavy metals that can cause severe health problems. Microcystins are toxic to the liver, while heavy metals like lead and mercury can cause long-term damage.

Spirulina may interact with and weaken the effects of immunosuppressants and blood-thinning medications. Anyone on these drugs should consult a doctor before use.

No, spirulina is not safe for everyone. It is contraindicated for those with certain medical conditions, and there is not enough evidence to confirm its safety for pregnant or breastfeeding women.

To minimize risks, only purchase spirulina from brands that provide third-party testing and certification for contaminants. Reputable brands grown in controlled environments are generally safer.

Yes, although it is not common, some people may have allergic reactions to spirulina. In severe cases, an anaphylactic reaction could occur. Individuals with other allergies may be at a higher risk of reacting to spirulina.