Other Name(s):

Algue Verte d'Eau Douce, Bulgarian Chlorella, Bulgarian Green Algae, Chinese Chlorella, Chlorella Algae, Chlorella pyrenoidosa, Chlorella vulgaris, Chlorelle, Clorela, Freshwater Green Algae, Freshwater Seaweed, Green Alga, Green Algae, Japanese Chlorella, Seaweed, Yaeyama Chlorella.


Chlorella is a type of algae that grows in fresh water. The whole plant is used to make nutritional supplements and medicine.

Most of the chlorella that is available in the U.S. is grown in Japan or Taiwan. It is processed and made into tablets and liquid extracts. These extracts contain "chlorella growth factor," which is described as a water-soluble extract of chlorella containing chemicals including amino acids, peptides, proteins, vitamins, sugars, and nucleic acids.

Be aware that chlorella products can vary significantly depending on the way “the crop” used to make them was cultivated, harvested, and processed. Investigators have found that dried preparation of chlorella can contain from 7% to 88% protein, 6% to 38% carbohydrate, and 7% to 75% fat.

As a medicine, chlorella is used for preventing cancer, reducing radiation treatment side effects, stimulating the immune system, improving response to flu vaccine, increasing white blood cell counts (especially in people with HIV infection or cancer), preventing colds, protecting the body against toxic metals such as lead and mercury, and slowing the aging process.

Chlorella is also used to increase “good” bacteria in the intestine in order to improve digestion; and to help treat ulcers, colitis, Crohn's disease, and diverticulosis.

Some people also use chlorella for the prevention of stress-related ulcers; treatment of constipation, bad breath, and hypertension; as an antioxidant; to reduce cholesterol; to increase energy; to detoxify the body; and as a source of magnesium to promote mental health, relieve premenstrual syndrome (PMS), and reduce asthma attacks. It is also used for fibromyalgia.

Chlorella is applied to the skin for treating skin ulcers, rashes caused by radiation treatment, and a sexually transmitted disease called trichomoniasis.

How does it work?

Chlorella is a good source of protein, fats, carbohydrates, fiber, chlorophyll, vitamins, and minerals. The cell wall of chlorella must be broken down before people can digest it.

Uses & Effectiveness

Insufficient Evidence to Rate Effectiveness for...

More evidence is needed to rate the effectiveness of chlorella for these uses.

Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, and Insufficient Evidence to Rate (detailed description of each of the ratings).


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Side Effects

Chlorella is POSSIBLY SAFE when taken by mouth, short-term (up to 2 months). The most common side effects include diarrhea, nausea, gas (flatulence), green discoloration of the stools, and stomach cramping, especially in the first week of use.

Chlorella has caused serious allergic reactions, including asthma and other dangerous breathing problems.

Chlorella can cause skin to become extra sensitive to the sun. Wear sunblock outside, especially if you are light-skinned.

Special Precautions & Warnings

Pregnancy and breast-feeding: There is not enough reliable information about the safety of taking chlorella if you are pregnant or breast feeding. Stay on the safe side and avoid use.

Iodine sensitivity: Chlorella can contain iodine. Therefore, chlorella might cause an allergic reaction in people sensitive to iodine.

Allergy to molds: Chlorella might cause an allergic reaction in people who are also allergic to molds.

Weak immune system (immunodeficiency): There is a concern that chlorella might cause “bad” bacteria to take over in the intestine of people who have a weak immune system. Be careful with chlorella if you have this problem.

“Autoimmune diseases” such as multiple sclerosis (MS), lupus (systemic lupus erythematosus, SLE), rheumatoid arthritis (RA), or other conditions: Chlorella might cause the immune system to become more active, and this could increase the symptoms of autoimmune diseases. If you have one of these conditions, it's best to avoid using chlorella.


Medications that decrease the immune system (Immunosuppressants)Interaction Rating: Moderate Be cautious with this combination.Talk with your health provider.

Chlorella might make the immune system more active. That could decrease the effectiveness of medications that are used to decrease (suppress) the immune system.

Some medications that suppress the immune system include azathioprine (Imuran), basiliximab (Simulect), cyclosporine (Neoral, Sandimmune), daclizumab (Zenapax), muromonab-CD3 (OKT3, Orthoclone OKT3), mycophenolate (CellCept), tacrolimus (FK506, Prograf), sirolimus (Rapamune), prednisone (Deltasone, Orasone), corticosteroids (glucocorticoids), and others.

Warfarin (Coumadin)Interaction Rating: Moderate Be cautious with this combination.Talk with your health provider.

Chlorella contains large amounts of vitamin K. Vitamin K is used by the body to help blood clot. Warfarin (Coumadin) is used to slow blood clotting. By helping the blood clot, chlorella might decrease the effectiveness of warfarin (Coumadin). Be sure to have your blood checked regularly. The dose of your warfarin (Coumadin) might need to be changed.


The appropriate dose of chlorella depends on several factors such as the user's age, health, and several other conditions. At this time there is not enough scientific information to determine an appropriate range of doses for chlorella. Keep in mind that natural products are not always necessarily safe and dosages can be important. Be sure to follow relevant directions on product labels and consult your pharmacist or physician or other healthcare professional before using.

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Reviewed on 6/14/2021

Antonian, A. A., Abakumova, I. A., Meleshko, G. I., and Vlasova, T. F. [Possibilities of using proteins from unicellular algae in biological life support systems]. Kosm.Biol Aviakosm.Med 1985;19(1):65-69. View abstract.

Basu, S., Salley, S. O., Whittlesey, G. C., and Klein, M. D. Feasibility studies for a photosynthetic artificial lung. Optimization of parameters affecting photosynthesis. ASAIO J 1994;40(3):M743-M746. View abstract.

Cheng, F. C., Lin, A., Feng, J. J., Mizoguchi, T., Takekoshi, H., Kubota, H., Kato, Y., and Naoki, Y. Effects of chlorella on activities of protein tyrosine phosphatases, matrix metalloproteinases, caspases, cytokine release, B and T cell proliferations, and phorbol ester receptor binding. J.Med.Food 2004;7(2):146-152. View abstract.

Chu, C. Y., Huang, R., and Ling, L. P. Purification and characterization of a novel haemagglutinin from Chlorella pyrenoidosa. J Ind Microbiol Biotechnol 2006;33(11):967-973. View abstract.

Csonto, J., Kadukova, J., and Polak, M. Artificial life simulation of living alga cells and its sorption mechanisms. J Med Syst. 2001;25(3):221-231. View abstract.

Gitelson, I. I., Terskov, I. A., Kovrov, B. G., Sidko, F. Y., Lisovsky, G. M., Okladnikov, Y. N., Belyanin, V. N., Trubachov, I. N., and Rerberg, M. S. Life support system with autonomous control employing plant photosynthesis. Acta Astronaut. 1976;3(9-10):633-650. View abstract.

Hagino, N. and Ichimura, S. [Effect of chlorella on fecal and urinary cadmium excretion in "Itai-itai" disease]. Nippon Eiseigaku Zasshi 1975;30(1):77. View abstract.

Hasegawa, T., Matsuguchi, T., Noda, K., Tanaka, K., Kumamoto, S., Shoyama, Y., and Yoshikai, Y. Toll-like receptor 2 is at least partly involved in the antitumor activity of glycoprotein from Chlorella vulgaris. Int.Immunopharmacol. 2002;2(4):579-589. View abstract.

Honek, L., Uzel, R., Fialova, L., and Sracek, J. [The use of a fresh-water weed Chlorella vulgaris for the treatment of the cervix after kryo-surgical interventions (author's transl)]. Cesk.Gynekol. 1978;43(4):271-273. View abstract.

Ichimura, S. [Effect of chlorella on skin cancer of Black Foot patients in south Formosa]. Nippon Eiseigaku Zasshi 1975;30(1):66. View abstract.

Ivanova, I. E., Derendiaeva, T. A., Alekhina, T. P., and Shaidorov, IuI. [The role of higher plants in the human biological life support system]. Kosm.Biol Aviakosm.Med 1990;24(4):40-43. View abstract.

Kameda, A. [Physiopathology of iron absorption from food in patients after partial gastrectomy, observation using F59-labeled chlorella]. Naika 1969;24(4):735-741. View abstract.

Kay, R. A. Microalgae as food and supplement. Crit Rev Food Sci Nutr 1991;30(6):555-573. View abstract.

Kralovec, J. A., Metera, K. L., Kumar, J. R., Watson, L. V., Girouard, G. S., Guan, Y., Carr, R. I., Barrow, C. J., and Ewart, H. S. Immunostimulatory principles from Chlorella pyrenoidosa--part 1: isolation and biological assessment in vitro. Phytomedicine 2007;14(1):57-64. View abstract.

Merchant, R. E. and Andre, C. A. A review of recent clinical trials of the nutritional supplement Chlorella pyrenoidosa in the treatment of fibromyalgia, hypertension, and ulcerative colitis. Altern.Ther.Health Med. 2001;7(3):79-91. View abstract.

Merchant, R. E., Andre, C. A., and Sica, D. A. Nutritional supplementation with Chlorella pyrenoidosa for mild to moderate hypertension. J.Med.Food 2002;5(3):141-152. View abstract.

Nakano, S., Noguchi, T., Takekoshi, H., Suzuki, G., and Nakano, M. Maternal-fetal distribution and transfer of dioxins in pregnant women in Japan, and attempts to reduce maternal transfer with Chlorella (Chlorella pyrenoidosa) supplements. Chemosphere 2005;61(9):1244-1255. View abstract.

Ng, T. P., Tan, W. C., and Lee, Y. K. Occupational asthma in a pharmacist induced by Chlorella, a unicellular algae preparation. Respir.Med. 1994;88(7):555-557. View abstract.

Ohkawa, S., Yoneda, Y., Ohsumi, Y., and Tabuchi, M. [Warfarin therapy and chlorella]. Rinsho Shinkeigaku 1995;35(7):806-807. View abstract.

Ohtake, T., Negishi, K., Okamoto, K., Oka, M., Maesato, K., Moriya, H., and Kobayashi, S. Manganese-induced Parkinsonism in a patient undergoing maintenance hemodialysis. Am J Kidney Dis 2005;46(4):749-753. View abstract.

Otles, S. and Pire, R. Fatty acid composition of Chlorella and Spirulina microalgae species. J.AOAC Int. 2001;84(6):1708-1714. View abstract.

Pugh, N., Ross, S. A., ElSohly, H. N., ElSohly, M. A., and Pasco, D. S. Isolation of three high molecular weight polysaccharide preparations with potent immunostimulatory activity from Spirulina platensis, aphanizomenon flos-aquae and Chlorella pyrenoidosa. Planta Med. 2001;67(8):737-742. View abstract.

Salisbury, F. B. Joseph I. Gitelson and the Bios-3 project. Life Support.Biosph.Sci 1994;1(2):69-70. View abstract.

Salisbury, F. B., Gitelson, J. I., and Lisovsky, G. M. Bios-3: Siberian experiments in bioregenerative life support. Bioscience. 1997;47(9):575-585. View abstract.

Schnitzler, S. and Rathsack, R. [Reaction of anti-A-hemagglutinin from Helix pomatia with algae (Chlorella pyrenoidosa) and demonstration of heterophilic agglutinins against algae in human sera]. Acta Biol.Med.Ger 1974;33(1):121-127. View abstract.

Walla, O. J., de Groot, E. J., and Schweiger, M. On the molecular mechanism of the circadian clock. The 41,000 M(r) clock protein of Chlorella was identified as 3-phosphoglycerate kinase. J.Cell Sci. 1994;107 ( Pt 2):719-726. View abstract.

Watanabe, F., Takenaka, S., Kittaka-Katsura, H., Ebara, S., and Miyamoto, E. Characterization and bioavailability of vitamin B12-compounds from edible algae. J Nutr Sci Vitaminol.(Tokyo) 2002;48(5):325-331. View abstract.

Wolf, L. Bioregeneration with maltose excreting Chlorella: system concept, technological development, and experiments. Adv.Space Biol.Med. 1997;6:255-274. View abstract.

Wu, L. C., Ho, J. A., Shieh, M. C., and Lu, I. W. Antioxidant and antiproliferative activities of Spirulina and Chlorella water extracts. J Agric.Food Chem 5-18-2005;53(10):4207-4212. View abstract.

Yamagishi, S., Nakamura, K., and Inoue, H. Therapeutic potentials of unicellular green alga Chlorella in advanced glycation end product (AGE)-related disorders. Med Hypotheses 2005;65(5):953-955. View abstract.

Davis DR. Some algae are potentially adequate sources of vitamin B-12 for vegans (letter, comment). J Nutr 1997;127:378,380.

Halperin SA, Smith B, Nolan C, et al. Safety and immunoenhancing effect of a Chlorella-derived dietary supplement in healthy adults undergoing influenza vaccination: randomized, double-blind, placebo-controlled trial. CMAJ 2003;169:111-7.. View abstract.

Jitsukawa K, Suizu R, Hidano A. Chlorella photosensitization. New phytophotodermatosis. Int J Dermatol 1984;23:263-8. View abstract.

Konishi F, Tanaka K, Himeno K, et al. Antitumor effect induced by a hot water extract of Chlorella vulgaris (CE): resistance to Meth-A tumor growth mediated by CE-induced polymorphonuclear leukocytes. Cancer Immunol Immunother 1985;19:73-8. View abstract.

Krcmery V Jr. Systemic chlorellosis, an emerging infection in humans caused by algae. Int J Antimicrob Agents 2000;15:235-7.. View abstract.

Merchant RE, Carmack CA, Wise CM. Nutritional supplementation with Chlorella pyrenoidosa for patients with fibromyalgia syndrome: a pilot study. Phytother Res 2000;14:167-73. View abstract.

Merchant RE, Rice CD, Young HF. Dietary Chlorella pyrenoidosa for patients with malignant glioma: effects on immunocompetence, quality of life, and survival. Phytother Res 1990;4:220-31.

Miyazawa Y, Murayama T, Ooya N, et al. Immunomodulation by a unicellular green algae (Chlorella pyrenoidosa) in tumor-bearing mice. J Ethnopharmacol 1988;24:135-46. View abstract.

Morimoto T, Nagatsu A, Murakami N, et al. Anti-tumor-promoting glyceroglycolipids from the green alga, Chlorella vulgaris. Phytochemistry 1995;40:1433-7. View abstract.

Ng TP, Tan WC, Lee YK. Occupational asthma in a pharmacist induced by chlorella, a unicellular algae preparation. Resp Med 1994;88:555-7.

Norman JA, Pickford CJ, Sanders TW, Waller M. Human intake of arsenic and iodine from seaweed-based food supplements and health foods available in the UK. Food Addit Contam 1988;5:103-9.. View abstract.

Peirce A. The American Pharmaceutical Association Practical Guide to Natural Medicines. New York, NY: William Morrow and Co., 1999.

Ruama AL, Torronen R, Hanninen O, Mykkanen H. Vitamin B12 status of long-term adherents of a strict uncooked vegan diet ("living food diet") is compromised. J Nutr 1995;125:2511-5. View abstract.

Tiberg, E., Rolfsen, W., Einarsson, R., and Dreborg, S. Detection of Chlorella-specific IgE in mould-sensitized children. Allergy 1990;45(7):481-486. View abstract.

Tyml R. Present state and possibilities of the medical use of chlorococcal algae. Acta Univ Palacki Olomuc Fac Med 1982;103:273-9.

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