Spirulina vs Chlorella
Spirulina versus chlorella: how the two microalgae differ, what meta-analyses of trials found, shared contamination and allergy cautions, and why no ranking is possible.
Content last updated . This page has not been medically reviewed.
Safety first. Natural products can cause side effects and interact with medicines. Read natural ingredient safety before you use anything on this page.
Spirulina and chlorella are sold side by side, but they are different organisms with different documented effects and cautions. In the best pooled trial data we read, neither one has been shown to be better overall. The right comparison depends on the outcome and on whether a product is clean and correctly labeled.
What each one is
"Spirulina" on a label usually means Arthrospira platensis Gomont, a cyanobacterium, sometimes called blue-green algae. Chlorella vulgaris Beij. is a green alga in a different group. [1] Names can mislead: a medical database entry titled "Spirulina" lists Aphanizomenon and "others" alongside Spirulina, so a product's Latin name matters. [2] The chlorella entry describes a fresh-water green alga. [3]
What research found
| Question | What the source found | Strength of evidence |
|---|---|---|
| Blood pressure and blood fats | A 2025 meta-analysis of randomized trials (12 on chlorella, 9 on spirulina) found chlorella had a neutral effect on blood pressure and blood fats. Spirulina was linked to a small drop in diastolic blood pressure, and the authors call the size small and of uncertain clinical significance. [4] | Chlorella: no good evidence of benefit in those outcomes. Spirulina: promising but limited |
| Head-to-head trial | Proper evidence not found in the sources we read for a randomized trial giving the same people spirulina and chlorella. We searched PubMed on 2026-10-23 for spirulina and chlorella randomized or comparison studies; results were animal feed, algae growing, an exercise review of mixed algae and the meta-analysis above, which analyzes each alga separately. | Not available |
| Spirulina safety rating | A US Pharmacopeia expert committee analyzed 31 adverse event reports and assigned a Class A safety rating to Spirulina maxima and S. platensis. [5] | Expert safety review |
Because the pooled results are for blood pressure and blood fats only, they say nothing about energy, immunity, detox or other things algae products are marketed for; those are marketing claims here.
Quality is the larger difference
A study of spirulina supplements sold in Slovenia found a high proportion (86.7%) of inappropriate declarations about elemental content, and noted that oversight of the supplement industry remains limited. [6] LactMed notes that supplements do not require extensive pre-marketing approval from the US FDA, that labeled and actual ingredients often differ, and that clinical results on one product may not apply to others. [3] See product quality and contamination.
Related pages
Spirulina and chlorella, Seaweed, sea moss and kelp and Heavy metals in natural ingredients.
Frequently asked questions
Are spirulina and chlorella the same thing?
No. Spirulina is usually Arthrospira, a cyanobacterium, and chlorella is a green alga. [1]
Which lowers blood pressure?
In one 2025 meta-analysis, spirulina was linked to a small drop in diastolic pressure of uncertain clinical significance and chlorella had a neutral effect. [4]
Can either contain harmful contaminants?
Yes, in some products. LactMed says spirulina grown in uncontrolled conditions can contain heavy metals, and some products can contain microcystins. [2]
Does chlorella interact with medicines?
LactMed says its high vitamin K content may decrease warfarin effectiveness. Ask a pharmacist about other medicines. [3]
Is there a winner?
No. In the pooled trial data neither is clearly ahead overall, and no head-to-head trial was found. [4]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Cautions that differ
- Spirulina: the LactMed entry says it is generally well tolerated when grown under controlled conditions, and that products grown in uncontrolled conditions can contain heavy metals and other contaminants. [2] Some products can be contaminated with a blue-green alga that produces liver toxins called microcystins. [2]
- Chlorella: the LactMed entry reports allergic reactions, including asthma and anaphylaxis, and photosensitivity after ingestion. It says chlorella's high vitamin K content may decrease warfarin effectiveness. [3]
If you take warfarin or another blood thinner, ask a pharmacist before using chlorella. See supplements and blood thinners and how interactions work.
Safety and who should ask first
Ask a clinician or pharmacist if you are pregnant or breastfeeding, giving a product to a child, have a liver or kidney condition, take blood thinners, or are due for surgery (tell the surgical team about any algae product). For an allergic reaction with trouble breathing or swelling of the face or throat, call 911. If someone swallowed a large amount or a child got into a product, call Poison Help at 1-800-222-1222.
References
- GBIF Secretariat. GBIF Backbone Taxonomy. Names checked 2026-10-23 through the GBIF species match service. Read 2026-10-23.
- Spirulina. Drugs and Lactation Database (LactMed). National Institute of Child Health and Human Development; entry dated 2021. Read 2026-10-23.
- Chlorella. Drugs and Lactation Database (LactMed). National Institute of Child Health and Human Development; entry dated 2021. Read 2026-10-23.
- Pinto-Leite M, et al. 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. Read 2026-10-23.
- Marles RJ, et al. United States Pharmacopeia safety evaluation of spirulina. Crit Rev Food Sci Nutr. 2011. Read 2026-10-23.
- Masten Rutar J, et al. Nutritional Quality and Safety of the Spirulina Dietary Supplements Sold on the Slovenian Market. Foods. 2022. Read 2026-10-23.