Can you take spirulina while breastfeeding?

What LactMed says

The National Library of Medicine’s own summary, quoted in full. We do not write a verdict of our own on this question, and we do not compress theirs into a label.

Spirulina (Aphanizomenon sp., Spirulina sp., and others) is a fresh-water blue-green alga that contains various nutrients such as protein, B vitamins, vitamin E, chlorophyll, beta-carotene, and iron. Spirulina has no specific lactation-related uses. No data exist on the excretion of any components of spirulina into breastmilk or on the safety and efficacy of spirulina in nursing mothers or infants. Spirulina is generally well tolerated when grown under controlled conditions. Minor adverse effects include diarrhea, bloating, upset stomach, flatulence, edema, headache, muscle pain, facial flushing, and sweating. Products that are grown in uncontrolled conditions can contain heavy metals and other contaminants. Some products can be contaminated with the blue-green algae species Microcystis aeruginosa, which produces the hepatotoxins called microcystins. Breastmilk discoloration, green in one case, has been reported.

Dietary supplements do not require extensive pre-marketing approval from the U.S. Food and Drug Administration. Manufacturers are responsible to ensure the safety, but do not need to prove the safety and effectiveness of dietary supplements before they are marketed. Dietary supplements may contain multiple ingredients, and differences are often found between labeled and actual ingredients or their amounts. A manufacturer may contract with an independent organization to verify the quality of a product or its ingredients, but that does not certify the safety or effectiveness of a product. Because of the above issues, clinical testing results on one product may not be applicable to other products. More detailed information about dietary supplements is available elsewhere on the LactMed Web site.

Quoted from Spirulina — Drugs and Lactation Database (LactMed®), National Institute of Child Health and Human Development, revised June 21, 2021.