Chlorella (Chlorella vulgaris): Uses, Evidence and Safety

Safety first: who should check before using chlorella

Chlorella is a food-like supplement, but a few people need to ask first. A US drug reference for breastfeeding (LactMed) says chlorella's high vitamin K content may make warfarin work less well, so anyone taking warfarin should talk to their prescriber or pharmacist before starting it. [1] The same entry says allergic reactions, including asthma and anaphylaxis, have been reported in people taking chlorella and in people preparing chlorella tablets, and that photosensitivity (skin reacting to sunlight) has occurred after eating it. [1] A 2025 scoping review of herbs that may stimulate the immune system listed chlorella among 15 with the most evidence of immune activation, so people with autoimmune conditions should ask their specialist first. [2] We did not find a source we could read that tests chlorella with transplant or other immune-suppressing medicines; that is not the same as "safe". See supplements and blood thinners, supplements and immunosuppressants and supplements before surgery. In an emergency (trouble breathing, swelling of the face or throat) call 911.

Overview

Chlorella is a single-celled green alga. The species most often sold is Chlorella vulgaris Beij., which GBIF lists as the accepted name, in the family Chlorellaceae. [3] Products are also sold under the name Chlorella pyrenoidosa; GBIF treats that name as a synonym of Auxenochlorella pyrenoidosa, so a label's Latin name may not match current botany. [3] LactMed describes chlorella as a fresh-water green alga containing carotenes, protein, fiber, vitamins, minerals and chlorophyll. [1] The part sold is the whole dried alga, as tablets, capsules or powder. Native range: not found in the sources we read. Chlorella is a different organism from spirulina, which is a blue-green cyanobacterium; see spirulina and chlorella and spirulina vs chlorella.

Traditional use (not proof of benefit)

We did not find a source we could read that describes traditional or historical medicinal use of chlorella, so we do not describe one. Most claims you see online ("detox", "immune boost", "energy") are marketing claims, not findings from trials; the table below shows what the research we read does and does not support.

What research shows

Most of the human trials below are small, short, and test different products and amounts, so a result for one product does not carry over to another. [4][13]

A 2026 narrative review says clinical findings on chlorella and spirulina are generally consistent but limited by differences in study design and product standardization. [14] Long-term outcomes such as heart attacks or deaths: Proper evidence not found in the sources we read.

Forms and why the form matters

Chlorella is sold as tablets, capsules and powder, and also as "extracts" or "growth factor" products. We did not read a source on how the tough cell wall changes what the body absorbs, so we make no claim about processed versus unprocessed products; a result for one product should not be assumed for another. [1] LactMed adds that dietary supplements do not require extensive pre-marketing approval by the US FDA and that labeled and actual ingredients often differ. [1] How much to use is a decision for a clinician or pharmacist, not this page.

Safety in more detail

• Common side effects: LactMed says chlorella is usually well tolerated but can cause nausea, diarrhea, abdominal cramps, gas and green stools. [1]
• Medicines: warfarin (high vitamin K content may reduce its effect). [1] Drugs that suppress the immune system, diabetes drugs, blood pressure drugs and thyroid medicines: Proper evidence not found in the sources we read. Because a scoping review lists chlorella among immune-stimulating supplements, ask about immune-suppressing medicines. [2] See how interactions work.
• Pregnancy: the small trial above reported benefit and safety in 10 women taking chlorella, which is too few to show safety. [7] Ask a midwife or doctor. See pregnancy and breastfeeding safety.
• Breastfeeding: LactMed says maternal chlorella intake is not expected to harm most breastfed infants and is probably acceptable; green breast milk has been reported. It also notes chlorella during pregnancy may lower dioxin content and raise some carotenes and immunoglobulin A in breast milk. [1]
• Children: Proper evidence not found in the sources we read.
• Liver and kidney: the sources we read give no liver or kidney warning for chlorella itself. A separate site page lists a kidney-diet source that names chlorella among supplements that can be high in phosphorus; see herbs and kidney disease. We did not read NIH LiverTox for chlorella.
• Iodine and thyroid: Proper evidence not found in the sources we read on chlorella's iodine content or thyroid effects. If you have a thyroid condition, see seaweed, iodine and thyroid and ask your clinician.
• Allergy: asthma and anaphylaxis have been reported, including in people handling the tablets. [1] See anaphylaxis and severe allergic reactions to natural products.
• Quality and contamination: a 2025 Polish study of 47 weight-loss supplements found the highest average mercury in chlorella products (21.58 micrograms per kg), still below the EU limit, though the authors still called a risk of side effects likely for some products. [11] A 2026 review calls cyanotoxin contamination of spirulina, Aphanizomenon and chlorella supplements an emerging concern with gaps on long-term human effects. [12] See heavy metals in natural ingredients and product quality and contamination.

Official statements

• LactMed (US National Library of Medicine, entry dated 2006 in PubMed): chlorella is usually well tolerated; allergic reactions, photosensitivity and a possible warfarin interaction are reported; probably acceptable during breastfeeding. [1]
• NCCIH, Memorial Sloan Kettering, EMA/HMPC: Proper evidence not found; we found no chlorella page at NCCIH or Memorial Sloan Kettering, and no EMA herbal monograph for chlorella in the sources we read.

Related pages

• Spirulina and chlorella
• Spirulina vs chlorella
• Greens powder side effects: vitamin K, heavy metals and medicine cautions
• Supplements and blood thinners
• Autoimmune conditions and immune-stimulating products
• Heavy metals in natural ingredients