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Blue-Green Algae (Spirulina)


Blue-green algae, of which spirulina is a well-known example, is a group of 1,500 species of microscopic aquatic plants. The two most common species used for human consumption are Spirulina maxima and Spirulina platensis. Spirulina is particularly rich in protein and also contains carotenoids, vitamins, minerals, and essential fatty acids.1

What Are Star Ratings?

This supplement has been used in connection with the following health conditions:

Used for Why
3 Stars
1 to 4.5 grams daily
Blue-green algae, or spirulina, helps promote reductions in weight, body fat, waist circumference, and triglyceride levels.
Blue-green algae, or spirulina, is a rich source of protein, vitamins, minerals, and essential fatty acids. It also provides antioxidant and anti-inflammatory phytochemicals, and one constituent from spirulina has been found to inhibit pancreatic lipase, a fat-digesting enzyme. In one placebo-controlled trial, 64 people with obesity took 1 gram of spirulina or placebo daily for 12 weeks; those taking spirulina lost 3.5 pounds and reported a significant decrease in appetite, while those taking placebo lost 1.4 pounds and reported increased appetite. Another placebo-controlled trial that included 52 subjects with overweight or obesity found 2 grams of spirulina daily taken during a 12-week reduced-calorie diet program reduced appetite and enhanced weight loss, body fat loss, and waist circumference reduction. In a multi-phase crossover trial, people with overweight or obesity had more improvement in body weight and fitness during a six-week exercise program if they were given 4.5 grams of spirulina daily compared to placebo, and the synergistic effect of spirulina and exercise was more profound in those with obesity. In addition, spirulina had positive impacts on body weight and some markers of fitness even in the absence of exercise. Comprehensive reviews and a meta-analysis of results from five controlled trials add further weight to findings that spirulina can reduce body weight, body fat, waist circumference, and appetite, and may have positive effects on cholesterol and triglyceride levels in people with overweight and obesity.

How It Works

How to Use It

Blue-green algae can be taken as a powder or as flakes, capsules, or tablets. The typical manufacturer’s recommended intake is 2,000–3,000 mg per day divided throughout the day. However, typical amounts shown to have helpful properties in animal studies would be equivalent to 34 grams per day or more, for a 150-pound human.

Where to Find It

Blue-green algae grow in some lakes, particularly those rich in salts, in Central and South America, and Africa. They are also grown in outdoor tanks specifically to be harvested for nutritional supplements.

Possible Deficiencies

As it is not an essential nutrient, blue-green algae is not associated with a deficiency state. However, people who do not consume several servings of vegetables per day could benefit from the carotenoids and other nutrients in blue-green algae. Since it is a complete protein, it can be used in place of some of the protein in a healthy diet. However, very large amounts are required to provide significant quantities of these nutrients from blue-green algae.


Interactions with Supplements, Foods, & Other Compounds

At the time of writing, there were no well-known supplement or food interactions with this supplement.

Interactions with Medicines

As of the last update, we found no reported interactions between this supplement and medicines. It is possible that unknown interactions exist. If you take medication, always discuss the potential risks and benefits of adding a new supplement with your doctor or pharmacist.
The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers’ package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a supplement with your doctor or pharmacist.

Side Effects

Side Effects

Few side effects have been reported from the ingestion of blue-green algae. However, as blue-green algae can accumulate heavy metals from contaminated water, consuming blue-green algae could increase the body’s load of lead, mercury, and cadmium,2 though noncontaminated blue-green algae have been identified.3 Another popular species of blue-green algae, Aphanizomenon flos-aquae, has been found to produce toxins.4 A few reports also describe allergic reactions to blue-green algae. Animal studies have found spirulina to be safe during pregnancy.5, 6, 7

There is one case report of a man who developed liver damage while taking spirulina.8 As he was also talking three prescription medications, it is not clear whether the spirulina caused or contributed to the liver injury.


1. Dillon JC, Phuc AP, Dubacq JP. Nutritional value of the alga Spirulina. World Rev Nutr Diet 1995;77:32-46.

2. Johnson PE, Shubert LE. Accumulation of mercury and other elements by spirulina (cyanophyceae). Nutr Rep Int 1986;34:1063-70.

3. Slotton DG, Goldman CR, Franke A. Commercially grown spirulina found to contain low levels of mercury and lead. Nutr Rep Int 1989;40:1165-72.

4. Elder GH, Hunter PR, Codd GA. Hazardous freshwater cyanobacteria (blue-green algae). Lancet 1993;341:1519-20 [letter].

5. Salazar M, Chamorro GA, Salazar S, et al. Effect of Spirulina maxima consumption on reproduction and peri- and postnatal development in rats. Food Chem Toxicol 1996;34:353–9.

6. Kapoor R, Mehta U. Effect of supplementation of blue green alga (Spirulina) on outcome of pregnancy in rats. Plant Foods Hum Nutr 1993;43:29–35.

7. Chamorro G, Salazar M. Teratogenic study of Spirulina in mice. Arch Latinoam Nutr 1990;40:86-94 [in Spanish].

8. Iwasa M, Yamamoto M, Tanaka Y, et al. Spirulina-associated hepatotoxicity. Am J Gastroenterol 2002;97:3212-3. [Letter]


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