Spirulina

A protein-rich blue-green algae, taken most often for antioxidants and weight.

People take it for

Antioxidants and inflammation
Weight and appetite
Cholesterol
Blood pressure
Exercise and recovery
Blood sugar

A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.

Compare spirulina prices per dose

What is spirulina?

Spirulina is a blue-green alga, a filamentous cyanobacterium rather than a plant, grown commercially and dried into a deep green powder. People have eaten it for a long time: it was gathered from Lake Texcoco and sold in the markets of Tenochtitlan in the sixteenth century. By dry weight it is mostly protein, and it also carries vitamins, minerals, omega-3 and omega-6 fats and a set of pigments, chief among them the blue protein phycocyanin. It is sold as pressed tablets and as loose powder.

Why do people take spirulina?

Antioxidants and inflammation

The thinking. Plenty of people take spirulina for nothing more specific than its antioxidants. The thinking is that its blue pigment phycocyanin, with its carotenoids and phenolic compounds, settles the reactive chemistry the body throws off and quietens the signals tissue sends out when irritated.

What research has found. This is measured in blood tests rather than in how anyone feels, and the markers move differently: reviews pooling several hundred adults found C-reactive protein a little lower and antioxidant capacity marginally higher, while interleukin-6, tumour necrosis factor and two markers of oxidative damage did not shift. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.

Weight and appetite

The thinking. Weight is one of the commoner reasons people reach for spirulina, usually a few tablets before a meal. The thinking is that a dense source of protein and micronutrients makes a reduced-calorie diet easier to hold to, and that it takes the edge off appetite.

What research has found. A review of twenty-three trials in 1,035 overweight and obese adults found an average fall in body weight, and two earlier poolings found the same for weight, waist and body fat, most of them alongside a calorie-controlled diet. A separate review, of growth in children and adolescents, found no clear difference. A fair body of trials has looked at this, and most point the same way.

Cholesterol

The thinking. Cholesterol and triglycerides are what many people go looking for a supplement about after a blood test. With spirulina the thinking rests on its pigments and its fats: that they act on how much fat the gut takes up from a meal, and on the fats already circulating.

What research has found. A meta-analysis of twenty trials in 1,076 people found lower LDL, total cholesterol and triglycerides and slightly higher HDL, and an earlier pooling of seven trials found the same pattern, tracking how long people took it rather than the dose. In one crossover trial the change showed mostly in the group that also exercised. This is one of the best-studied uses, and several reviews of trials broadly agree.

Blood pressure

The thinking. Blood pressure often brings people to spirulina later in life, usually after a reading at the surgery. The idea follows from the antioxidant one: that if the lining of the blood vessels is under less oxidative strain, the vessels stay a little more supple.

What research has found. Pooled results in a few hundred adults point to small average falls, roughly four to five millimetres of mercury in the upper reading and less in the lower one, clearest where pressure was already raised or where it was taken for over eight weeks. Research here is still young: a few studies so far, mostly pointing the same way.

Exercise and recovery

The thinking. Hard training throws off reactive molecules and leaves muscle sore and stiff for a day or two afterwards. Some people take spirulina around their sessions on the thinking that its pigments take the edge off that chemistry, so the next session comes round sooner.

What research has found. In elite rugby players, markers of muscle damage and inflammation rose after an exhausting fitness test only in the group on a dummy capsule; in recreationally trained men put through a damaging session, soreness and strength were no different. A review of thirteen studies noted better exercise tolerance at easier efforts, and no gain in power sports. The studies disagree, so this is unsettled: dose, duration and who took part all seem to shift the result.

Blood sugar

The thinking. Blood sugar is the other number people come away from a check-up thinking about, and spirulina turns up in routines built around it. The thinking is that the pigments and polysaccharides that act on the fats in the blood also act on how the body answers insulin.

What research has found. Trials in adults with metabolic syndrome, obesity or type 2 diabetes found lower fasting glucose and better insulin sensitivity, and a three-month trial alongside a prescribed diabetes medicine found a fall in HbA1c. Nearly everyone studied already had a diagnosis. Only a few studies have measured this so far, though they mostly agree.

What does spirulina do in the body?

Spirulina is not a plant but a cyanobacterium, and what you swallow is the whole dried organism rather than an extract of one part of it. The parts researchers keep returning to are its pigments: phycocyanin, the blue protein that gives it its colour, and beta-carotene.

In laboratory and animal work those pigments scavenge free radicals, slow the oxidation of fats and raise the activity of the body’s own antioxidant enzymes, superoxide dismutase and catalase; they also act on the signalling pathways that turn inflammation up and down. Two things complicate the picture: reviewers describe a threshold above which more spirulina stops adding antioxidant activity, and phycocyanin is an unstable protein, which is why so much research goes into extracting and storing it.

What do people say about taking spirulina?

These are anecdotes people have shared, not evidence.

What people like

The five threads sit in different places: two parenting boards, two long-term-illness communities and a triathlon forum, so the reasons vary widely.
Some describe more energy or less tiredness, and in two of the threads that was the reason they started taking it at all.
Several take it as a protein or general nutrient top-up rather than for any one effect, usually stirred into a smoothie.
Three describe staying on it for months or longer without trouble, one through three pregnancies and one for a full year.

Common complaints

The taste and the smell put people off in most of the threads; they call it unpleasant and hide it in juice or berries.
Tablet size is a recurring gripe: two describe them as very large, and one crushes them between spoons to get them down.
Several took it for weeks, months or in one case a whole year and noticed nothing at all, good or bad.
A few report stomach upset, aching or an irritated bladder within days of starting and stopped; one put it down to the protein.

How people take it

Powder stirred into a smoothie or juice is the commonest way, often with banana or dark berries to cover the flavour.
Tablet takers count out several at a time: three to six a day is usual, and one athlete goes far higher in heavy training.
Several pair it with chlorella, another algae, in the same routine, which makes it hard to say which one is doing what.
A couple start small and build up; the amounts named run from two tablets a day to twenty, and one poster twenty grams of powder.

Read from these public discussions:

Spirulina for weight loss (Mumsnet, 2023)
Spirulina worry (Mumsnet, 2016)
Spirulina (MS Society forum, 2013)
Spirulina (Slowtwitch triathlon forum, 2012)
Chlorella and spirulina reaction, anybody? (Phoenix Rising ME/CFS forum, 2012)

What forms of spirulina are there?

Form	What’s different	Per serving, on products we list
Tablets	Dried whole algae pressed into tablets or filled into capsules, so each one holds a fixed amount.	500 mg to 2 g
Powder	The same dried algae loose and unpressed, deep blue-green, measured by the spoon into a drink.	not in our price tables yet

What else is worth knowing about spirulina?

Trials have used between one and eight grams a day, most often for eight to twelve weeks; the ones that name a tablet count used two to four 500 mg tablets daily, so a serving on a label may be more than one tablet.
A two-week trial gave a high dose of a pigment-rich extract, about a gram of phycocyanin a day, to look at bleeding risk: markers of platelet activation and three measures of clotting were unchanged.
Almost all of the trials were in adults who were overweight or already had raised blood pressure, blood sugar or cholesterol, several while on prescribed medicines.
One review reports that the research so far suggests spirulina is safe in healthy adults, and that those trials used supplements rather than spirulina-containing foods.

If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.

The research behind this page (37 studies)

How much does spirulina cost?

That depends on the form and the pack, so we work out the price of the same dose of every spirulina product we can find and rank them.

Compare spirulina prices per dose