Doctor's Note

For more on chlorella, check out Treating Hepatitis C with Chlorella.

Also check out my other videos on spirulina and blue-green algae supplements. 

For further context, see my associated blog post: The Best Foods: test your nutrition knowledge.

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  • Michael Greger M.D.

    There are also videos on spirulina and blue-green algae supplements. Please feel free to leave any questions below and I’d be delighted to answer them.

  • Michael Greger M.D.

    I am forever indebted to The Healthy Librarian (check out her excellent blog Happy Healthy Long Life) for correcting my confusion of chlorella phylogeny. I had mistakenly lumped chlorella in with blue-green algae, and they’re not even in the same biological kingdom! Unlike cyanobacteria (spirulina and blue-green algae such as Klamath Lake Aphanizomenon flos-aquae), chlorella does not appear to produce muscle, nerve, or liver toxicity.

  • It isn’t playing for me right now.
    But it did still take over that dog’s body, right?

    • Michael Greger M.D.

      Are you still having problems viewing the video? Live chlorella can indeed infect humans and animals, but what we buy in stores is dried and dead and therefore harmless (but you still might not want to take dips in scummy ponds with open wounds).

  • Toxins

    Doesn’t the Chlorella Growth Factor call for some concern in humans? Wouldnt this be similar to IGF, promoting unnecessary growth of our bodies?

    • Michael Greger M.D.

      I’ve never even heard of that! Do you know if that’s just some marketing ploy or a real entity? I couldn’t find anything in the National Library of Medicine database under that name. But if you can find out what it’s really called (if it indeed even exists) I’d be happy to hunt down info about it.

      • Bob

        IGF – Insulin-like Growth Factor, very popular among the bodybuilding industry

        • b00mer

          Hi Bob, I think he was asking about the “Chlorella Growth Factor”. Dr. Greger has definitely heard of IGF!

    • elsie blanche

      You have raised an interesting possibility. Have you come to any conclusions or obvious reasons to avoid ingesting chlorella, in regards to IGF similarities? I have always had some concerns with chlorella, and would not be surprised to see a study in the future showing negative attributes, yet many vegans just adore and have gratitude for the product.

  • Toxins

    Maybe it is just made up by the marketers. their selling point was that it quadruples in size everyday so it would aid in tissue repair.

  • Aramis

    Dr. Greger,
    I am currently going through a Detox therapy due to some heavy metals contamination (G.I. Tract, etc – mainly Hg – Mercury). Chlorella was prescribed by my M.D./Biochemist Nutritionist/and Nutritionist both Ph.D). I was surprise to see on your DVD #5 that your recommendation was to stay away from it due to BMAA bacteria. In my research some companies test to ensure their product is BMAA tested. Do you still recommend to stay away from it. My levels of Hg are coming down and I haven’t even started to do DMPS yet.
    Thank You!
    Aramis Ortiz
    San Diego, CA

    • Michael Greger M.D.

      As I note in the subtitle above, chlorella does not have the toxins which may be present in blue-green algae supplements ( and spirulina (

      • Kartoffelmao

        In this video on spirulina; you say that chlorella has brain toxins… care to elaborate on this?

        • I added a note to that video–no brain toxins in chlorella (I meant to say blue-green algae). I’m going to re-record the video to correct the error–thank you so much for pointing that out!

    • Gary Birch

      Gary Birch-Spain
      Have you checked facebook on the Detox Agency, or maybe even, you could even look at the Gerson Therapy web site for detox information and guidance.

  • Aramis

    Note: In the analysis done it showed that I have Mercury, Aluminum, Lead, and Arsenic. Natural chelation with Chlorella and cilantro is one process. Synthetic aminoacid such as DMPS and DMSA is another method. I also did a one week Sauna Detox.
    Again Thank You!
    Aramis Ortiz
    San Diego, CA

  • Jazzie

    If any algae is grown hydroponically do you still have to worry about toxins? If spiralina is grown hydroponically can I take it along with chlorella?
    Thank you in advance for your advice.

    • Toxins

      The issue is not with how the spirulina is grown but what byproducts are produced by it. Therefore it shouldn’t matter how the spirulina is grown.

  • Michael Greger M.D.

    For some context, please check out my associated blog post The Best Foods: Test Your Nutrition Knowledge!

  • Javier

    Recently I have read an article that have create on me confusion about cholorella. This article, which source is natural news, was explaning that most of the cholorella that we consume comes from China, Japan and Korea has a very high concentration of Aluminiun. Have you heard something about it? Do you have some information, research that prove this fact or clarify a litlle bit this issue. Wre live in World that we do not know who we trust even brands that they are bio they are doing funny things and at the end they get money through or most precious give our health. I would appreciate all the information you can share with us.
    Thank you.

  • Eric P

    Does Chlorella have enough iodine to meet a person’s daily requirement? I am taking .5-1 tablespoon of chlorella a day.

  • barbarabrussels

    Dear Dr Greger,
    Thanks for all your hard work. Blue-green algae are out, but how are we to know the colour of the algae in vegan omega 3 supplements ? Would you happen to know if they are safe here in Europe, i.e. toxin-free? Thank you.
    Ps Your work deserves international recognition, the whole world should benefit from it. A suggestion: I have a degree in translation, say I were to translate one of your transcripts into Dutch, would you be able to use it in any way? Or is it too soon for such a leap?
    Gratefully yours,

    • Diane Burgin

      Omega 3 supplements from algae are made from golden algae

  • Lyndia

    Spirulina is not known to have any toxins or to affect the liver…. that is AFA from Klamath Lake…. they are not the same.. US grown Spirulina is always clean… not so if it comes from China (Chlorella has the same issue of toxins when it comes from China) Dr. Christopher Hills (the father of Spirulina) was the primary researcher of Chlorella for 12 years (he had the Chlorella International Union) along with his partner Dr. Hiroshi Nakumara… they shifted their research & promotion to Spirulina when it was found to be much more compatible with the human body…. and to have more nutrition to boot. I have been marketing, studying & taking Spirulina for 32 years… I can’t say enough about what it does for the human body. Now with Fukushima, it is imperative that we get it out to as many people as possible…. it is one of the few algae’s that have medical research/practice on the positive effects it has on people who have radiation exposure.

  • priscilla

    I started taking some chlorella from china which was supposed to be grown and purified in a lab. Everything was fine for about 5 weeks then I noticed after about 2 hours of taking it, I would vomit. This happened 3 times, about a week apart, while I backed off taking the chlorella in the days between. The last time I was pretty sick. I haven’t taken it since. The literature said if something like that happened that a person taking the chlorella should increase the dose, even though it didn’t seem logical—their comments,not mine. It said the body was detoxifying and finally getting rid of stuff. I wasn’t under a doctor’s supervision and felt if I took it anymore, I didn’t know what would happen. Any thoughts about reactions to this product?

    • XenaSharon

      I think it sounds more like that your body had had enough of the Chlorella. I think that when the body has had enough of something, whether it be certain kinds of food which may or may not agree with you, even chocolate, you will start to feel sick, perhaps even vomit, if you try and eat more and more of it. I don’t think it’s a sign of the body “finally detoxifying itself”. And I don’t think it means you should start eating more of what is making you feel sick. I think it is the body saying it has had enough of whatever you have been consuming.

  • NotYetAVegan

    According to, Chlorella is a viable source of B12 for vegans.
    Can you confirm or deny?

    • Joseph Gonzales R.D.

      Many of the algae mimic the cobalamin (B12) structure, but they are not absorbed like B12 and cannot be relied on as a B12 source.

  • Julie Someone

    it took me a long time.. like over 5 years to get to the ending of this video…i just can’t stop laughing….. ~~~ i love to laugh ~~~ thank you :-D

  • antony

    how do you suggest for best spirulina ?
    the name of this product ideal . Thank

  • Stephie.H.

    I recently suggested my mother takes Chlorella but it makes her vomit terribly. She is on Enalapril for high blood pressure, Sorvasta for Cloresterol and Levothyroxine for thyroid. Could it be reacting with any of these?

  • Your last comment that “Kale is cheaper” begs the question: but does chlorella offer any enhanced benefits that we wouldn’t get from Kale? I’m specifically wondering about improved recovery from endurance running. Do you know if there are any studies or reasons to believe one way or another? Also, how do we make sure we are buying a safe brand?

  • Cathy Alder

    We are a plant based family and I was wondering if a Chlorella supplement is something I should consider giving my teenaged children.

  • Dear dr. Gregor and his team,
    I am in desperate need of your help. I have been introduced to an article from National library of medicine (which many find as a trustworthy source), that suggests that chlorella could be a viable source of vitamin B12 for us, vegans. Many of us would welcome this option, because eating this vegetable sounds better than taking synthetic supplements, but we want to be sure, that its safe that way. We trust you and your knowledge, so I ask you for advice in this matter.
    The article:
    Thank you for everything you do, your work has helped me a lot.
    Yours sincerely,
    Daniel Kostić

  • Thea

    Daniel Kostic: Your post got caught in the spam filter. I just released it. Hopefully someone who can address your question will be able to now.

    • Thank you, Thea. I am looking forward to that. Have a beautiful day.

  • NFmoderatorRenae

    Sounds promising from this study, however I think one of the main issues is that the doses are less clear, and the products are often mixed with other algae, such as spirulina, which have inactive B12 analogues…

  • Claudia T.

    What is with the toxine Microcystine, which is dangerous und for the liver and kidney. The WHO warns. Now I don´t what I can doing and eliminate all toxins (Amalagan) Mercury? Or can I take Kale?

  • Rene

    Can I use chlorella as a dietary source of DHA and EPA?
    If no, why not?