Blue-Green Algae Supplements: Microcystins and Quality
Blue-green algae supplements (AFA, spirulina): what microcystins are, what testing found, the Oregon 1 mcg/g limit, who should ask first, and what to ask a seller.
Content last updated . This page has not been medically reviewed.
"Blue-green algae" is a loose name for supplements made from cyanobacteria, tiny organisms that live in water and look like algae. Some of these products are fine and some have been found to carry a natural liver toxin from other bacteria that grow beside them. This page explains what was found, what the numbers mean, and what you can reasonably ask a seller. It is information, not a recommendation to take or avoid any product.
Read this first
- Some blue-green algae products have contained microcystins, liver toxins. In the 2000 Gilroy study, 85 of 87 products tested had some, and 63 were over the 1 mcg/g limit Oregon had set. [1]
- The risk depends on the product and where it was harvested, not on the word "algae". Lake-harvested AFA has the most test data showing contamination. Products made only from spirulina or chlorella showed no microcystin in the 2018 survey we read that tested them. [2]
- Tell a clinician before using these products if you are pregnant or breastfeeding, giving one to a child, have an autoimmune disease or PKU, or take blood thinners, diabetes medicines or immune-suppressing medicines. [4][5][6][7]
- Signs of possible liver trouble (dark urine, yellow skin or eyes, unusual tiredness) need prompt medical care. [5]
- For an allergic reaction with trouble breathing or swelling of the face or throat, call 911 or your local emergency number.
What "blue-green algae" means
Blue-green algae are cyanobacteria. Three names get mixed up:
| Name on the label | What it is | Where to read more |
|---|---|---|
| AFA, Klamath algae, Aphanizomenon flos-aquae | A cyanobacterium harvested from lakes, for example Upper Klamath Lake in Oregon. [1] | More about AFA, Klamath algae, Aphanizomenon flos-aquae → |
| Spirulina, Arthrospira | A cyanobacterium, usually grown in controlled ponds or tanks. | Spirulina and Spirulina and chlorella explained |
| Chlorella | Not a cyanobacterium. It is a green alga in a different group. | More about Chlorella → |
Chlorella is sometimes lumped in because it is also sold as a green powder. Our comparison page covers the differences: spirulina vs chlorella. This page does not repeat what trials found for spirulina or chlorella; it is about contamination and quality.
Microcystins and other cyanotoxins
Microcystins are toxins made by some cyanobacteria, notably Microcystis. Memorial Sloan Kettering describes them as ring-shaped peptides that cause liver damage, and warns that contaminated products may cause liver damage, kidney failure, nerve damage, seizures and breathing failure; it lists these as possible harms from cyanotoxin contamination, not as common results. [4]
How they get into a product: AFA is harvested from a lake where Microcystis aeruginosa also blooms, and the toxin-making species can be collected by accident. [1] Cultivated spirulina in controlled ponds is a different situation. Health Canada's drinking-water document names contaminated natural health products, including algal supplements, as a possible source of exposure, though drinking water is the main one. It sets no supplement limit in the part we read. [8]
What testing has found
| Study or source | What was tested | What it found |
|---|---|---|
| Gilroy and colleagues, Environmental Health Perspectives, 2000 | 87 blue-green algae products, most containing AFA | Microcystins in 85 of 87; 63 (about 72%) above 1 mcg/g; microcystin-LR, the most toxic form, seemed most common. The authors say health risks from these foods had been largely ignored. [1] |
| Marsan and colleagues, Heliyon, 2018 | 51 dried AFA products, plus spirulina-only and chlorella-only products as comparison | 26 of 51 AFA products (51%) were above the test kit's 0.25 mcg/g detection limit; four were above 1.0 mcg/g (1.1 to 2.8). Spirulina-only and chlorella-only products showed none detectable. [2] |
| Health Canada survey (second-hand) | Natural health products | A summary we found reports no microcystin in spirulina-only products and high intakes from some non-spirulina products. We could not read the original, so we do not rely on it. |
Two cautions. These are samples of products on sale at a given time, so they do not describe any single brand today. And the 2018 study found that serving sizes on labels ranged from 0.5 to 15 g a day, so how much toxin a person actually gets depends on the product and the portion. [2]
BMAA: what the sources say, and do not say
BMAA is a compound some researchers have worried about in connection with nerve disease. Results for spirulina products disagree. A 2014 study of 10 spirulina-containing products found no BMAA with two methods (detection limits 80 and 93 ng/g), and called the result reassuring but preliminary. [3] A search summary also pointed to other reports that did detect small amounts, but we did not read those, so we do not describe them as findings. Whether BMAA in supplements affects health: proper evidence not found in the sources we read.
Quality testing and seals
- What a lab can check: that a batch is under a stated microcystin level. The 2018 study validated a test kit against a more precise lab method (LC-MS/MS) for dried products. [2]
- What a seal does not do: NCCIH says words like "certified" or "verified" do not necessarily guarantee product quality or consistency. [7] Check what the seal actually tests for, and whether it covers microcystins. For a general explanation, see third-party testing for herbal products.
- Regulation: the FDA generally cannot review supplements for safety before they are sold and can act only after a problem appears. [7] Harvard Health also notes there is no guarantee a spirulina product is free of contaminants or contains the labeled amount. [6]
What you can reasonably ask a seller
- Which organism is it (AFA, spirulina, or a blend), and where was it grown or harvested: a controlled pond or a wild lake?
- Does each batch get tested for microcystins, and what limit is used (1 mcg/g is the Oregon figure)?
- Can they show a recent batch result (a certificate of analysis) for your lot number?
- If a seal is on the label, what does the seal test for? Does it include microcystins and heavy metals?
- What is the serving size on the label? (Labels in one study ranged from 0.5 to 15 g a day. [2])
A seller who cannot answer these is not proof of a bad product, but it tells you how much you can know about it.
Related pages
Frequently asked questions
Is spirulina the same as blue-green algae?
Spirulina is one kind of blue-green algae (a cyanobacterium). The name is also used for AFA and blends. Chlorella is not a blue-green alga. [1][2]
What is the Oregon limit for microcystins?
Oregon set 1 mcg/g for blue-green algae products. [1] A 2018 paper says it was accidentally dropped from Oregon's rules and not yet re-adopted when it was written, so check the current rule. [2]
Did the Gilroy study show these products are dangerous?
It found microcystins in 85 of 87 products and 63 above Oregon's limit. [1] It tested products, not people, and does not tell you about any brand sold today.
Can I avoid microcystins by choosing spirulina?
In the 2018 survey we read, spirulina-only products showed no detectable microcystin. [2] That is not a guarantee for every product.
Do seals prove a product is safe?
No. NCCIH says words like "certified" or "verified" do not necessarily guarantee quality or consistency. Ask what is tested. [7]
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.
The Oregon limit and what regulators say
- Oregon: after a 1996 bloom, the state health and agriculture agencies set a limit of 1 mcg/g of microcystin in blue-green algae products. [1] The 2018 paper says the limit was based on an assumed adult intake of about 2 g/day, was accidentally dropped from Oregon's rules, and that re-adoption proposed in 2015 had not been finalized when it was written. [2] We could not read the current Oregon rule, so check with the Oregon Health Authority before relying on it.
- United States (federal): no federal microcystin limit for these products, but manufacturers must set and test specifications for contaminants. The authors suggest many manufacturers use 1 mcg/g as their own limit. [2]
- Children: the 2018 authors note that the limit was not designed for children. [2]
- Health Canada: no supplement limit found in the document we read. Its drinking-water numbers (1.5 mcg/L, and 0.4 mcg/L as a reference for mixing infant formula) are for water, not supplements. [8]
Who should ask first
| Group | What the sources say |
|---|---|
| Pregnant or breastfeeding | WebMD says it is not known how blue-green algae affect pregnancy, and that contaminants such as microcystins are possible. [5] MSKCC reports a case of a newborn with seizures linked to the mother's long-term spirulina use. [4] |
| Children | Health Canada's older advice against giving these products to children is known to us only second-hand. NCCIH notes that many supplements have not been tested in children or in pregnancy. [7] |
| Autoimmune disease (lupus, rheumatoid arthritis, multiple sclerosis) | WebMD and Harvard Health say the algae may stimulate the immune system and could worsen symptoms. [5][6] MSKCC says there is no evidence that immune effects seen in one healthy-adult study help fight infection. [4] |
| PKU (phenylketonuria) | Blue-green algae contain phenylalanine, so people with PKU should check first. [5][6] |
| Medicines | WebMD lists blood thinners, diabetes medicines and immune-suppressing medicines as ones to discuss; it says interactions are not fully understood. [5] MSKCC says spirulina inhibits two liver enzymes (CYP 1A2, 2E1) and the clinical importance is not known. [4] See supplements and blood thinners. |
| Other | MSKCC lists anaphylaxis and one case of rhabdomyolysis (severe muscle breakdown) as reported effects. [4] |
References
- Gilroy DJ, Kauffman KW, Hall RA, Huang X, Chu FS. Assessing potential health risks from microcystin toxins in blue-green algae dietary supplements. Environ Health Perspect. 2000;108(5):435-439. Abstract read 2026-10-24.
- Marsan DW, Conrad SM, Stutts WL, Parker CH, Deeds JR. Evaluation of microcystin contamination in blue-green algal dietary supplements using a protein phosphatase inhibition-based test kit. Heliyon. 2018;4(3):e00573. Read 2026-10-24.
- McCarron P, Logan AC, Giddings SD, Quilliam MA. Analysis of BMAA in spirulina-containing supplements by liquid chromatography-tandem mass spectrometry. Aquat Biosyst. 2014;10:5. Read 2026-10-24.
- Memorial Sloan Kettering Cancer Center. Blue-green algae. About Herbs. Read 2026-10-24.
- WebMD. Blue-green algae. Read 2026-10-24.
- Harvard Health Publishing. By the way, doctor: Is spirulina good for you?. June 21, 2021. Read 2026-10-24.
- National Center for Complementary and Integrative Health. Using Dietary Supplements Wisely. Read 2026-10-24.
- Health Canada. Guidelines for Canadian Drinking Water Quality: Guideline Technical Document, Cyanobacterial Toxins. First 100,000 characters read 2026-10-24.