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SupplementScience

Spirulina Side Effects & Safety

Reviewed by·PharmD, BCPS

This content is for informational purposes only and does not constitute medical advice. Consult your healthcare provider before starting any supplement. Full disclaimer

Safety Profile

Overall safety rating: Generally Safe

Potential Side Effects

  • Mild GI discomfort (nausea, bloating) — most common, especially at higher doses or initial use
  • Green discoloration of stool (harmless)
  • Headache reported rarely, usually resolves with dose reduction
  • Allergic reactions in individuals sensitive to algae or seaweed
  • Contamination risk — spirulina harvested from uncontrolled environments may contain heavy metals, microcystins, or bacteria; always choose quality-tested brands

Drug & Supplement Interactions

  • Immunosuppressants (cyclosporine, azathioprine, methotrexate) — spirulina stimulates immune function and may counteract immunosuppressive therapy
  • Anticoagulants (warfarin, heparin) — contains vitamin K which may reduce anticoagulant efficacy; also has mild antiplatelet effects
  • Diabetes medications — may potentiate blood sugar lowering effects; monitor glucose
  • Antihypertensives — spirulina may modestly lower blood pressure; additive effect possible
  • Phenylketonuria (PKU) medications — spirulina contains phenylalanine

Maximum Dose

Do not exceed: 8g/day (doses up to 19g/day have been used in short-term studies without serious adverse effects)

Full Spirulina Guide

References

  1. Huang H, Liao D, Pu R, Cui Y (2018). Quantifying the effects of spirulina supplementation on plasma lipid and glucose concentrations, body weight, and blood pressure. Diabetes, Metabolic Syndrome and Obesity. DOI PubMed
  2. Romay Ch, González R, Ledón N, Remirez D, Rimbau V (2003). C-phycocyanin: a biliprotein with antioxidative, anti-inflammatory and neuroprotective effects. Current Protein & Peptide Science. DOI PubMed
  3. Selmi C, Leung PS, Fischer L, German B, Yang CY, Kenny TP, Cysewski GR, Gershwin ME (2011). The effects of Spirulina on anemia and immune function in senior citizens. Cellular & Molecular Immunology. DOI PubMed
  4. Cingi C, Conk-Dalay M, Cakli H, Bal C (2008). The effects of spirulina on allergic rhinitis. European Archives of Oto-Rhino-Laryngology. DOI PubMed
  5. Ou Y, Lin L, Yang X, Pan Q, Cheng X (2013). Antidiabetic potential of phycocyanin: effects on KKAy mice. Pharmaceutical Biology. DOI PubMed
  6. Finamore A, Palmery M, Bensehaila S, Peluso I (2017). Antioxidant, immunomodulating, and microbial-modulating activities of the sustainable and ecofriendly spirulina. Oxidative Medicine and Cellular Longevity. DOI PubMed
  7. Mazokopakis EE, Papadomanolaki MG, Fousteris AA, Kotsiris DA, Lampadakis IM, Ganotakis ES (2014). The hepatoprotective and hypolipidemic effects of Spirulina (Arthrospira platensis) supplementation in a Cretan population with non-alcoholic fatty liver disease. Turkish Journal of Gastroenterology. PubMed