Spirulina is a biomass of cyanobacteria (blue-green algae) that can be consumed by humans and other animals. The two species are Arthrospira platensis and A. maxima.

Cultivated worldwide, Arthrospira is used as a dietary supplement or whole food. It is also used as a feed supplement in the aquaculture, aquarium, and poultry industries.

The U.S. National Institutes of Health describes spirulina supplements as “possibly safe”, provided they are free of microcystin contamination, but “likely unsafe” (especially for children) if contaminated.

Like all protein-rich foods, spirulina contains the essential amino acid phenylalanine (2.6-4.1 g/100 g), which should be avoided by people who have phenylketonuria, a rare genetic disorder that prevents the body from metabolizing phenylalanine, which then builds up in the brain, causing damage. Heavy-metal contamination of spirulina supplements has also raised concern. The Chinese State Food and Drug Administration reported that lead, mercury, and arsenic contamination was widespread in spirulina supplements marketed in China.

Spirulina was a food source for the Aztecs and other Mesoamericans until the 16th century; the harvest from Lake Texcoco in Mexico and subsequent sale as cakes were described by one of Cortés’ soldiers.
As an ecologically sound, nutrient-rich dietary supplement, spirulina is being investigated to address food security and malnutrition, and as dietary support in long-term space flight or Mars missions. Spirulina was successfully used by NASA as a dietary supplement for astronauts on space missions.

In 1974, the World Health Organization described spirulina as “an interesting food or super food” for multiple reasons, rich in iron and protein, and is able to be administered to children without any risk,” considering it “a very suitable food.” It is well understood that deficiency of nutrients is responsible for changes in immunity, studies suggest that Spirulina may modulate the immune system by its role in covering nutritional deficiencies.

A more recent study administered Spirulina supplements in ischemic heart disease patients and found a significant reduction in blood cholesterol.
spirulina extract plus zinc twice daily for 16 weeks may be useful for the treatment of chronic arsenic poisoning with melanosis and keratosis.
Spirulina is a safe food supplement without significant side-effects but its role as a drug remains to be seen.