We do not sell spirulina. Not in any form, not as an ingredient in anything. So this is one of the few pages here where we have nothing to gain from what it says, which is the right frame for what follows.
An earlier version of this article was one of the worst things on this site. It recommended a product that contains no spirulina, gave a dose range up to five times higher than anything studied, and listed conditions spirulina supposedly helps manage. All of that is gone and the corrections are below.
What spirulina actually is
Spirulina is not a plant and not a seaweed. It is a cyanobacterium, a photosynthetic bacterium that grows in warm alkaline water and takes its name from its spiral shape. That it is usually shelved beside seaweed products is a supermarket decision rather than a biological one.
It has been eaten for centuries. The Aztecs harvested it from Lake Texcoco and it is still gathered from Lake Chad. In 1974 the United Nations described it as a promising future food, mostly for the reason below.
As food production goes it is remarkable: high protein per unit of land and water, grown without arable soil, in conditions where little else grows. That is the genuinely interesting fact about spirulina and it has nothing to do with supplements.
What is in it, with the serving size attached
Spirulina is roughly 55 to 70 percent protein by dry weight, and carries B vitamins, iron, beta-carotene, magnesium, and the blue pigment phycocyanin.
The number that matters is the serving. Most of the impressive percentages you will read are per 100 grams, and nobody eats 100 grams of spirulina. A typical serving is a teaspoon to a tablespoon, 3 to 7 grams, which delivers about 2 to 4 grams of protein. That is real, and it is a fraction of an egg.
So: a nutritious ingredient, not a meaningful protein source, and not a substitute for eating vegetables.
On the word "detox"
Here is the part the original article had backwards.
Your liver and kidneys are not waiting for assistance. They are not a filter that clogs, and there is no residue accumulating in you that a supplement clears out. When "detox" appears on a label it almost always means one of three ordinary things: you are eating less, you are drinking more water, or you are having a laxative effect.
There is a real clinical meaning of the word, used for lead or mercury poisoning and for withdrawal, and it involves a hospital rather than a smoothie.
None of this makes spirulina pointless. It makes it food. A nutritious ingredient added to a diet is a good thing on its own terms and does not need a mechanism invented for it.
The contamination story, running the correct direction
Spirulina does not remove heavy metals from your blood. The earlier version of this article said it did, in those words, and that is simply not something it does.
The documented issue is the reverse. Spirulina is grown in open water and takes up what is in that water. Poorly sourced product has been found carrying lead, mercury and cadmium, and, more seriously, microcystins, toxins produced by other cyanobacteria that can grow alongside it in an uncontrolled pond.
This is not obscure or contested. It is the single most important thing to know before buying spirulina, and it is why sourcing matters more for this supplement than for almost anything else on a shelf.
What to look for: a named growing location, third-party testing, and explicit testing for microcystins. If a seller cannot tell you where it was grown, that is your answer.
How much people actually take
Studied intakes are commonly 1 to 3 grams a day, with the upper end of the trial literature around 10 grams. Start low. There is no benefit established for large amounts, and the rule that more is better does not hold for anything grown in open water.
The earlier version of this page recommended up to 15 grams a day and set a ceiling of 50. Both figures were wrong and the second was reckless.
Who should not take it
- Anyone with phenylketonuria. Spirulina is high in phenylalanine. - Anyone pregnant or nursing, not because of a known problem but because the contamination risk above is not one worth accepting on incomplete information. The original article recommended it in pregnancy, which it should not have. - Anyone on prescription medication, without asking a clinician first.
The correction we owe readers
The old version of this article recommended Restoriix as its spirulina product, including in a smoothie recipe.
Restoriix contains no spirulina. It is activated charcoal and zeolite, and its own fact sheet specifies a two-hour gap from any medication, because activated charcoal binds things in the gut indiscriminately, medicines included. Putting it in a daily smoothie on our recommendation was a genuine error and we are sorry for it.
If you want the seaweed compound this site does write about properly, that is fucoidan, and the wider picture is in Seaweed 101, which is also where spirulina gets correctly filed as not being seaweed.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.
More on this subject: Fucoidan & Seaweed