Is spirulina dangerous?

Spirulina is a cyanobacterium renowned for its many nutritional and therapeutic benefits. Its richness in vitamins, minerals, antioxidants and proteins makes it a superfood. There are, however, a number of precautions that should be followed to avoid any risks. Find out more about our recommendations for consuming spirulina, as well as the contraindications and side effects of this blue micro-algae.

By Stéphanie Catrysse

Updated on 7/24/2025Reading time: 0 min.

Spirulina: everything you need to know

Spirulina is a filamentous cyanobacterium, often referred to as a micro-algae, and is one of the oldest living organisms on Earth. It is renowned for its exceptional nutritional properties and is used as a food supplement. Here are some key characteristics of spirulina:

Origin and cultivation: spirulina grows naturally in the warm, alkaline waters of certain tropical and subtropical lakes. It is now grown in tanks specially designed for commercial production.
Nutritional composition: spirulina is rich in protein (around 60-70% of its dry weight), vitamins (including B1, B2, B3, B6, B9, C and E), minerals (iron, calcium, magnesium, zinc and potassium) and essential fatty acids such as omega-6. It also contains beneficial pigments such as chlorophyll and phycocyanin.
Uses and benefits: thanks to its high nutritional value, spirulina is used to improve endurance, boost the immune system, detoxify the body and supplement vegetarian and vegan diets.
Forms of consumption: spirulina is available as a powder, tablet or capsule, or incorporated into foods such as energy bars and drinks.

Recommendations for taking spirulina: frequency, dosage

Spirulina can be taken internally or externally in a variety of forms. Powder, flakes, capsules, or tablets – it's up to you to choose the form that suits you best.

According to recommendations, internal consumption of spirulina should not exceed 5 g per day in a repeat 1 to 3-month course of treatment. The ideal amount is therefore between 1 and 5 g per day, depending on your needs. It is best to start your course of spirulina with small quantities, then gradually increase.

We recommend that you always choose organic spirulina, to guarantee that it is good quality.

What are the side effects of spirulina?

When consumed in the recommended quantities, and when the dose is increased gradually throughout the course of treatment, spirulina has no side effects.

We do, however, advise you to avoid taking spirulina in the evening, as it can have a stimulating effect on some people who have difficulty sleeping.

Warning: if taken in excess or too much at the start of a course of treatment, spirulina can cause skin rashes, bloating, abdominal pain, disordered bowel functions, dark or greenish stools, muscle pain, migraines and even a slight fever. If one or more of these symptoms appear at the start of a course of treatment, reduce the dose sharply for several days before slowly and gradually increasing it again. If in doubt, ask your doctor for advice.

If you take too much, spirulina can weaken the kidneys and liver, so always follow the recommended dosage.

Spirulina and medicines: are there any interactions?

There are no known contraindications to combining spirulina with medicines or plants.

As a precautionary measure, we recommend that you seek your doctor's advice if you are taking any particular treatment.

As far as phytotherapy is concerned, spirulina can easily be combined with other plants such as rhodiola, ginseng, ginger or turmeric to boost its natural stimulating properties, or chlorella to combine their detoxifying properties.

What are the contraindications to taking spirulina?

Despite its wide range of medicinal and nutritional properties, spirulina has a number of contraindications.

It is not recommended for people suffering from:

Haemochromatosis (excess iron in the blood) due to its high iron content;
Phenylketonuria due to its phenylalanine content;
Kidney failure or gout (excess uric acid) due to its high protein content;
Autoimmune diseases (rheumatoid arthritis, multiple sclerosis, etc.) due to its immunostimulant properties;
Allergy to seaweed.

If you are affected by one or more of these conditions, it is essential that you seek advice from your doctor.

Find out more

Spirulina is very rich in antioxidants that are precursors of vitamin A (including beta-carotene). In the '90s, some scientific studies raised concerns about a possible increased risk of lung cancer for smokers consuming beta-carotene. The health authorities then restricted the recommended daily intake. But these studies did not distinguish between dietary beta-carotene (naturally present in spirulina, for example) and synthetic beta-carotene (based on retinol). Since then, numerous studies have been carried out, showing that consumption of this antioxidant food supplement poses no risk to smokers below a threshold of 15 mg per day (which is very high).

Spirulina, consumed in the recommended doses, therefore presents no risk to smokers. On the contrary, it is detoxifying, immunostimulating and remineralising.

Spirulina, often wrongly considered to be an algae, does not grow in a marine environment. It is in fact a cyanobacterium that initially grows in brackish water, but is now cultivated in controlled freshwater basins. Unlike conventional algae, it contains no iodine, so poses no risk in the event of thyroid disease. It does not interfere with products commonly prescribed for thyroid problems.

During pregnancy or when breastfeeding, there is no specific recommendation against taking spirulina. But as a precaution and because there are so few studies on the subject, we advise pregnant or breastfeeding women to seek medical advice before consuming spirulina.

Focus on our Naturopathic editor, Stéphanie Catrysse

Stéphanie Catrysse is a naturopath (certified by the FENA), a wellness massage and lymphatic drainage practitioner, and a personal development consultant.

Passionate about alternative medicine, she practices a holistic approach to health.