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Herb library · Seaweed · Arthrospira platensis, A. maxima

Spirulina

A dried blue-green alga (really a cyanobacterium) sold as a protein- and nutrient-rich powder. It may lower blood pressure a little; the main risk is contamination of poorly grown products with liver toxins or heavy metals.

Serious warning

Spirulina grown in uncontrolled conditions can be contaminated with heavy metals or with other blue-green algae that make microcystins, which are liver toxins (LactMed, LiverTox). LiverTox rates spirulina a possible rare cause of liver injury.

Traditional use

Spirulina grows in warm, alkaline lakes and has been eaten for centuries by people in Mexico and Central America. It is up to 65 to 70% protein and rich in vitamins, iron and the blue pigment phycocyanin. Commercial supplements are recent, sold to counter unintended weight loss and for ADHD, hay fever, high blood pressure, diabetes, stress, fatigue, anxiety and depression.

What studies show

  • Limited

    Blood pressure: a 2024 meta-analysis of randomized trials found spirulina lowered systolic pressure by about 4 mmHg and diastolic by about 3 mmHg, more in people with high blood pressure or overweight. The authors rate the evidence moderate and call for larger, better trials.

  • Insufficient

    Allergies, diabetes, fatigue, mood and other uses: LiverTox says studies in people are limited and spirulina has not been proven effective for any medical condition.

Be careful of

Cautions

  • NoteGenerally well tolerated when grown under controlled conditions. Minor side effects include diarrhea, bloating, upset stomach, gas, swelling, headache, muscle pain, flushing and sweating.
  • ConditionOne published case described hepatitis 5 weeks after starting spirulina, which cleared after stopping it (along with other drugs that can harm the liver). Stop and see a clinician if you notice dark urine or yellow skin or eyes.
  • PregnancyNo data exist on spirulina in breastfeeding. One mother's milk turned green after she took an algae blend.
  • NoteBuy from makers who test for microcystins and heavy metals; LiverTox notes that the purity of products implicated in liver injury has not been reported.
  • Ask a clinicianTalk with a clinician or pharmacist before using this if you take prescription medicines, are pregnant or breastfeeding, or are giving it to a child.

Sources

  1. Spirulina (LiverTox) (opens in a new tab) · NIH · read September 25, 2026
  2. Spirulina (LactMed) (opens in a new tab) · NIH · read September 25, 2026
  3. The Effect of Spirulina Supplementation on Blood Pressure in Adults: A GRADE-Assessed Systematic Review and Meta-Analysis (2024) (opens in a new tab) · NIH · read September 25, 2026

Reviewed September 25, 2026.