Chlorella: what is it and is chlorella safe?
Short answer: Chlorella is a green, single-celled freshwater alga that you buy as tablets or powder. In the EU it is an ordinary, permitted food. Is chlorella dangerous? For most people it is not, but there are points to watch: chlorella contains vitamin K (important if you take blood thinners such as warfarin or acenocoumarol), quality varies per product and there are old reports of skin reactions in sunlight. If you are pregnant, breastfeeding or take medication, talk to your GP or pharmacist first.
Last updated: 5 November 2026 · Written by Florian Fermin
"Is chlorella safe?" is a search we see a lot. That makes sense: online you read a lot of big promises, and then you also want to know the downsides.
Below you can read what chlorella is, which species is in our products, what is known about safety and when to check with your doctor first. The difference with spirulina is covered in spirulina vs chlorella.
What is chlorella?
Chlorella is a green, single-celled freshwater alga. It is so small that you can only see it under a microscope and it owes its deep green colour to chlorophyll. For tablets, the alga is grown, harvested, dried and pressed. In French it is called chlorelle, in Dutch and German chlorella.
Chlorella has a cellulose cell wall. You cannot digest it when it is intact, which is why the cell wall is mechanically broken in most supplements (Bito et al., 2020). From the 1950s onwards, chlorella was used as food mainly in Japan and later sold worldwide as a supplement.
In the EU, chlorella is not a novel food. Chlorella vulgaris, Chlorella pyrenoidosa and related species are listed in the European Commission's Novel Food Catalogue as "not novel in food": they were already eaten in the EU before 15 May 1997 (EU Novel Food Catalogue; European Commission, 2022).
Which chlorella is in our products?
The species differs per product. Here we name what is on the current product page:
- Chlorella Tablets 500 mg Organic: Chlorella pyrenoidosa, 500 mg per tablet, 300 tablets.
- Spirulina Chlorella Tablets 500 mg Organic: Chlorella vulgaris, together with spirulina. 250 mg of each per tablet.
- Chlorella & Spirulina Tablets Combo Deal: one jar of Chlorella Tablets and one jar of Spirulina Tablets.
In the EU catalogue, the name Chlorella pyrenoidosa is now also listed as Auxenochlorella pyrenoidosa, because the classification of chlorella species has been revised. For the legal status this makes no difference.
Is chlorella dangerous?
No, chlorella is not dangerous for most healthy adults if you stick to the daily dose. We did not find large studies on side effects with long-term use. What has been described, I list below.
| Point to watch | What is known | What to do |
|---|---|---|
| Vitamin K and blood thinners | Chlorella contains vitamin K. In a case report, warfarin worked less well after chlorella. | Do you take a vitamin K antagonist? Check first with your anticoagulation clinic or pharmacist. |
| Quality and heavy metals | Algae can contain heavy metals. The composition depends on how the alga was grown. | Choose a product with a certificate of analysis (CoA). |
| Skin and sunlight | In Japan, five people were described in 1984 with skin reactions on sun-exposed skin after chlorella tablets, caused by the substance pheophorbide a. | If you get skin complaints in the sun, stop and talk to your GP. |
| Iodine | Chlorella is a microalga with little iodine. Iodine is mainly a concern with seaweed. | If you have thyroid problems, check with your doctor before using any algae or seaweed product. |
| PKU | Like any protein source, chlorella contains phenylalanine. | Check with your doctor or dietitian. |
| Pregnant, breastfeeding, medication | The packaging says to consult your doctor first in that case. | Talk to your GP or pharmacist first. |
Every described side effect, and how strong the evidence is, is covered in chlorella side effects.
Chlorella and blood thinners: why vitamin K matters
Chlorella contains vitamin K, and that matters if you take a blood thinner that works via vitamin K. According to a review, commercial chlorella products contain vitamin K (Bito et al., 2020).
In a Japanese case report from 1995, the blood clotting of a 75-year-old man who was well controlled on warfarin was inhibited less after he started taking chlorella. There was no sign that he had stopped his medication or was getting vitamin K from medicines or natto. The doctors describe chlorella as a vitamin K-rich food that can reduce the effect of warfarin (Ohkawa et al., 1995). It concerns one patient, but the mechanism is well known.
Vitamin K antagonists include warfarin, acenocoumarol and phenprocoumon. If you take one of these and want to start or stop chlorella, tell your doctor or anticoagulation clinic, so your dose can be adjusted if needed.
Does chlorella contain iodine?
Chlorella contains little iodine. The Verbraucherzentrale Hamburg describes chlorella as a microalga with little iodine. Iodine is mainly a concern with seaweed (macroalgae), where the content can vary widely (Verbraucherzentrale Hamburg, 2025; Voedingscentrum).
Our label does not state an iodine content. If you have a thyroid condition or take thyroid medication, talk to your doctor before you start using algae or seaweed products. You can read more about seaweed in our sea moss guide.
Heavy metals in chlorella: what to look for
With chlorella, look for a certificate of analysis (CoA) in which heavy metals and microbiology have been tested. Algae can contain heavy metals such as cadmium and lead (Verbraucherzentrale Hamburg, 2025), and the composition of chlorella varies greatly by growing method and species (Bito et al., 2020). In the EU, maximum levels apply to food supplements for lead, cadmium and mercury, among others (Regulation (EU) 2023/915).
- Ask for a CoA with lead, cadmium, mercury and arsenic.
- Check which species is on the label and how many milligrams per tablet.
- Choose a short ingredient list. Our chlorella tablets contain only organic chlorella.
You can request a CoA for our chlorella tablets via support@getgoyu.com.
Skin reactions in the sun: what is pheophorbide?
Pheophorbide a is a breakdown product of chlorophyll that can make the skin more sensitive to sunlight. In 1984, Japanese dermatologists described five people who developed swelling and red patches on skin that had been in the sun after taking chlorella tablets. They identified pheophorbide a and a related substance in the tablets as the cause (Jitsukawa et al., 1984).
These are old reports and we did not find recent cases. If you do get skin complaints in places exposed to the sun after taking chlorella, stop and talk to your GP.
How much chlorella per day?
There is no official recommended amount for chlorella. Our Chlorella Tablets say: "Take 3 tablets twice per day with water. Preferably during or just after a meal." That is 6 tablets of 500 mg, 3 grams per day in total, and a jar of 300 tablets lasts 50 days.
In the human studies discussed by Bito et al., participants usually received 5 to 10 grams of chlorella per day, for a few weeks to three months (Bito et al., 2020). That says something about what has been studied, not about what you should take. Stick to the label.
As for what chlorella does: the EU has not authorised any health claims for chlorella itself. What is allowed are these claims for our chlorella tablets: Chlorella is naturally high in protein** and Protein contributes to the maintenance of muscle mass**.
**Authorised health claim (Regulation (EU) No 432/2012) or nutrition claim (Regulation (EC) No 1924/2006).
Want to combine chlorella with spirulina? Then read spirulina vs chlorella. What spirulina is and how much of it to take is explained in what is spirulina.
The dosage per product and the amounts used in research are covered in chlorella dosage.
Summary in 3 points
- Chlorella is a green, single-celled freshwater alga and an ordinary food in the EU, not a novel food.
- For most people chlorella is not dangerous. Watch out for vitamin K if you take a vitamin K antagonist, for quality (CoA) and for skin reactions in the sun.
- Our packaging says 3 tablets twice a day, 3 grams in total. Talk to your doctor first if you are pregnant, breastfeeding or take medication.
Frequently asked questions
What are the side effects of chlorella?
We did not find large studies on side effects. What has been described is a reduced effect of warfarin due to vitamin K and, in old Japanese reports, skin reactions in the sun caused by pheophorbide a. If you get complaints, stop and talk to your GP.
Can I take chlorella with blood thinners?
Check with your doctor, anticoagulation clinic or pharmacist first, especially with warfarin, acenocoumarol or phenprocoumon. Chlorella contains vitamin K, and that can affect how these medicines work.
How many chlorella tablets per day?
Our packaging says 3 tablets of 500 mg, twice a day, with water and with a meal. That is 3 grams of chlorella per day. Do not go above that amount.
Is chlorella a novel food?
No. Chlorella vulgaris, Chlorella pyrenoidosa and related species are listed in the EU catalogue as "not novel in food", because they were already eaten in the EU before 1997. So they may simply be used in foods and supplements.
Chlorella tablets or powder?
Both contain dried chlorella. Tablets are easier if you don't like the taste of algae and want to dose precisely. We only sell chlorella as tablets. What to look for when choosing them is covered in chlorella tablets: what to look for.
Sources
- Bito T, Okumura E, Fujishima M, Watanabe F. Potential of Chlorella as a dietary supplement to promote human health. Nutrients. 2020;12(9):2524. doi:10.3390/nu12092524 (review; two authors work for a chlorella producer)
- Ohkawa S, Yoneda Y, Ohsumi Y, Tabuchi M. Warfarin therapy and chlorella. Rinsho Shinkeigaku. 1995;35(7):806-807. PubMed 8777808 (case report, 1 person)
- Jitsukawa K, Suizu R, Hidano A. Int J Dermatol. 1984;23(4):263-268. doi:10.1111/j.1365-4362.1984.tb01245.x (case reports, 5 people)
- Verbraucherzentrale Hamburg. Algen essen: Auf den Jodgehalt achten, 4 February 2025. vzhh.de
- Voedingscentrum (Dutch Nutrition Centre). Zeewieren en algen. voedingscentrum.nl
- European Commission. Novel Food Catalogue, entries Chlorella vulgaris (POL-NF-00242) and Chlorella pyrenoidosa (POL-NF-00240): not novel in food. food.ec.europa.eu
- European Commission. Novel food status consultation Chlorella sp., 2022. food.ec.europa.eu
- Commission Regulation (EU) 2023/915 on maximum levels for certain contaminants in food. eur-lex.europa.eu
- Product pages and packaging texts of Chlorella Tablets and Spirulina Chlorella Tablets, consulted 5 November 2026.
You can find all our chlorella tablets on the page buy chlorella. Looking for spirulina or sea moss too? You can find all our algae together in our algae supplements.
This article is for information only and is not medical advice. Food supplements are not a substitute for a varied and balanced diet and a healthy lifestyle. If in doubt, pregnant or taking medication, talk to your GP or pharmacist.
Chlorella from GOYU
Organic 500 mg tablets: on their own, together with spirulina in one tablet or as a combo deal.
