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Moderate evidenceHeart & metabolic

Spirulina

Small trials fairly consistently show lipid and blood-pressure improvements, and the pooled effect sizes are large enough to be suspicious — nearly every trial is small, short, and from a handful of research groups. A real signal sitting on a weak evidence base.

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What the science says

  • Blood lipids Moderate evidence

    A meta-analysis of 7 RCTs reported total cholesterol -46.8 mg/dL (95% CI -67.3 to -26.2), LDL -41.3 mg/dL, triglycerides -44.2 mg/dL, and HDL +6.1 mg/dL. Those effects rival statins, which should make you cautious rather than excited: the trials were small, largely conducted in dyslipidemic populations, and often not placebo-controlled. Benefit correlated with duration, not dose.

  • Blood pressure Moderate evidence

    Pooling 5 RCTs in 230 subjects taking 1-8 g/day for 2-12 weeks, spirulina lowered systolic BP by 4.59 mmHg (95% CI -8.20 to -0.99, I2 = 65%) and diastolic BP by 7.02 mmHg (95% CI -8.86 to -5.18, I2 = 11%), with the effect concentrated in hypertensive subgroups. The systolic estimate is heterogeneous and the total evidence base is only a few hundred people.

  • Exercise performance and fatigue Limited evidence

    A handful of small trials report improved time to exhaustion and reduced exercise-induced oxidative markers at 2-6 g/day. These are underpowered, not independently replicated, and not sufficient to recommend spirulina as an ergogenic aid.

Dosage & safety

Studied dose1-8 g/day. Cardiometabolic trials most often used 1-4.5 g/day for 8-12 weeks; blood pressure trials ranged 1-8 g/day for 2-12 weeks. There is no evidence that higher doses work better — pooled lipid effects were independent of dose.
SafetyThe main hazard is contamination, not the algae itself: wild-harvested or poorly controlled spirulina can carry microcystin hepatotoxins, BMAA, or heavy metals, so third-party-tested product matters more than brand. Absolutely contraindicated in phenylketonuria — spirulina is very high in phenylalanine. Theoretical concern in autoimmune disease because it stimulates cytokine production; caution with immunosuppressants. Contains vitamin K (relevant to warfarin) and pseudo-vitamin B12 that assays as B12 but is not bioavailable to humans — never use spirulina as a B12 source, particularly on a vegan diet.

How to take it

TimingTiming does not matter.
With food?Take it with food to reduce nausea.
Worth knowingBuy only third-party-tested product - microcystin hepatotoxin contamination is the real risk with spirulina and you cannot see, smell or taste it.

Interactions

With medications

  • warfarin

    Spirulina contains vitamin K, which opposes warfarin and can drop your INR. keep your intake constant and tell your prescriber, or avoid it

  • ciclosporin, tacrolimus and other immunosuppressants

    Spirulina stimulates cytokine production, which theoretically opposes immunosuppression. do not combine on immunosuppressive therapy

With other supplements

  • vitamin B12

    Spirulina's pseudo-B12 registers on assays but is not bioavailable, so it can mask a genuine deficiency. take a real B12 supplement separately and never count spirulina toward your intake

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does spirulina lower cholesterol?

Spirulina has moderate evidence for lowering cholesterol: a meta-analysis of 7 small trials reported large drops in total cholesterol, LDL and triglycerides. Effects that rival statins should make you cautious, since the trials were small, often not placebo-controlled and from a few research groups.

Does spirulina lower blood pressure?

Pooling 5 trials in 230 people taking 1-8 g/day of spirulina found lower systolic and diastolic blood pressure, mainly in people with hypertension. The evidence is moderate but rests on only a few hundred participants.

Is spirulina a good source of vitamin B12 for vegans?

No: spirulina contains pseudo-B12 that shows up on assays but is not bioavailable to humans, and it can mask a genuine deficiency. Never count spirulina toward your B12 intake; take a real B12 supplement.

Is spirulina safe?

The main spirulina hazard is contamination with microcystin liver toxins, BMAA or heavy metals, so buy only third-party-tested product. Spirulina is absolutely contraindicated in phenylketonuria, its vitamin K can lower INR on warfarin, and it should not be combined with immunosuppressants.

Scientific references

Where to buy

Frontier Co-op, Organic Spirulina Powder, 16 oz (453 g)

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