Spirulina
Summary
Spirulina is a protein-rich cyanobacterium. Meta-analyses found it lowered blood pressure (grade C), but a 2025 review saw only a small diastolic drop and no clear lipid effect. Some algae supplements tested positive for liver toxins (microcystins) above tolerable limits, so product quality matters. Trials used 1 to 8 g a day.
Key facts
- A dried cyanobacterium (Arthrospira) sold as a protein- and pigment-rich supplement[2]
- A 2016 meta-analysis of 7 trials reported large cholesterol drops, but a 2025 review of 9 trials found no significant lipid effect[3][2]
- 8 of 18 algae supplements (spirulina or Aphanizomenon) contained cyanotoxins above tolerable daily intake[5]
- 1 to 8 g a day for 2 to 12 weeks in the blood pressure trials[1]
- 2 graded human outcomes on this page
- October 11, 2026
How it works
ProposedSpirulina supplies protein and pigments such as phycocyanin with antioxidant activity in lab studies; how it might lower blood pressure in people is not established.[2]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Blood pressure and lipids | Mixed | Grade C | Meta-analysis · n = 299 · 2025 Adults in 9 spirulina trials (101–299 per outcome) Form: Spirulina · Dose: Varied across trials · Duration: Varied Diastolic pressure fell slightly (SMD −0.42); total cholesterol showed a non-significant trend; the authors called the effect small and of uncertain clinical significance. | 40289965 (opens PubMed)Source [2] |
| Blood pressure | Improved | Grade C | Meta-analysis · n = 230 · 2021 Adults in 5 randomized trials, including people with hypertension Form: Spirulina · Dose: 1–8 g/day · Duration: 2–12 weeks Systolic −4.6 mmHg and diastolic −7.0 mmHg, mainly in people with hypertension. | 34578932 (opens PubMed)Source [1] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Spirulina powder or tablets | Varies[1][5] | No head-to-head human absorption data between products in our sources.[1][5] | Generally well tolerated in trials; contamination with cyanotoxins is the main product-quality concern.[1][5] | Blood pressure and lipids (1–8 g/day) |
Studied doses
Doses studied in human trials ranged from 1 to 8 g of spirulina a day for 2 to 12 weeks.[1]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
None found in our sources.
Who should be careful
- Anyone buying untested products
- Several algae supplements contained microcystins and other cyanotoxins above tolerable limits; look for third-party toxin testing.[5]
- Breastfeeding
- LactMed notes that blue-green algae can be contaminated with microcystins, liver toxins, and that supplement contents are not verified before sale.[6]
- People on blood pressure medicine
- Pooled trials show lower blood pressure, which could add to these drugs; no interaction studies are cited here.[1]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Where to buy Spirulina
Products from brands we partner with that contain Spirulina. Listing a product is not a claim that it works; check the amount per serving against the doses studied above, and the label for other ingredients.
- SupersmartPaid linkSpirulina 500 mg8 tablets: 4,000 mg spirulina (500 mg per tablet); 30 servingsShop at Supersmart (opens in new tab)Price and label checked 2026-10-11 on the brand’s site.
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- Offer terms from Supersmart’s site and its affiliate program, checked Oct 8, 2026. Offers can change; the brand's checkout is final.
Frequently asked questions
Does spirulina lower blood pressure?
A meta-analysis of 5 trials found drops of about 4–7 mmHg, mostly in people with hypertension; a later review found a smaller effect.[1][2]
Does spirulina lower cholesterol?
An older meta-analysis said yes, but a 2025 review of 9 trials found no significant effect.[3][2]
Is spirulina safe?
Trials report good tolerance, but some algae supplements contained liver toxins, so tested products matter.[5]
How much spirulina was studied?
Trials used 1 to 8 g a day.[1]
Sources
- [1]Effect of Spirulina Supplementation on Systolic and Diastolic Blood Pressure: Systematic Review and Meta-Analysis of Randomized Controlled Trials.. Nutrients, 2021. meta-analysis
- [2]The Role of Chlorella and Spirulina as Adjuvants of Cardiovascular Risk Factor Control: A Systematic Review and Meta-Analysis of Randomised Controlled Trials.. Nutrients, 2025. meta-analysis
- [3]A systematic review and meta-analysis of the impact of Spirulina supplementation on plasma lipid concentrations.. Clin Nutr, 2016. meta-analysis
- [4]Effects of Spirulina supplementation on obesity: A systematic review and meta-analysis of randomized clinical trials.. Complement Ther Med, 2019. meta-analysis
- [5]Detection of Cyanotoxins in Algae Dietary Supplements.. Toxins (Basel), 2017. observational
- [6]Spirulina., 2006. database
What changed
- Effect arrows corrected on 1 row(s): outcomes where a harmful measure fell (pain, symptoms, blood pressure, lipids, glucose, risk) now show as improved (up). No study data changed.
- First draft. Every PMID checked against NCBI E-utilities (title, year and journal taken from the PubMed record) and abstracts read for each cited row. Product details in Where to buy read from the brand page on the date shown. Self-reviewed in a second strict pass (no independent reviewer yet).