Chlorella (Chlorella pyrenoidosa) is a type of algae that grows in fresh water. It's sometimes called seaweed. It's used for nutrition and as medicine.

Chlorella is a good source of protein, fats, carbohydrates, fiber, chlorophyll, vitamins, and minerals. Most of the chlorella that is available in the U.S. is grown in Japan or Taiwan. It's made into tablets and liquid extracts.

Chlorella is used to prevent low levels of iron during pregnancy. It is also used for depression, menstrual cramps, fibromyalgia, high cholesterol, and other conditions, but there is no good scientific evidence to support many of these uses.
When taken by mouth: Chlorella is likely safe when used for 2-3 months. The most common side effects include diarrhea, nausea, gas, green stools, and stomach cramping. Chlorella can also make the skin extra sensitive to the sun. Wear sunblock outside, especially if you are light-skinned.

When applied to the skin: There isn't enough reliable information to know if chlorella is safe or what the side effects might be.

Special Precautions & Warnings:

Pregnancy: Chlorella is possibly safe when taken by mouth for up to 28 weeks, starting during the second trimester of pregnancy.

Breast-feeding: There isn't enough reliable information to know if chlorella is safe to use when breast-feeding. Stay on the safe side and avoid use.

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

Weak immune system (immunodeficiency): Chlorella might cause "bad" bacteria to take over in the intestine of people who have a weak immune system. Use caution if you have a weakened immune system.

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


NatMed Pro rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.
Likely effective Effectiveness definitions
Possibly effective Effectiveness definitions
  • Low levels of iron during pregnancy. Chlorella contains small amounts of iron. Taking chlorella by mouth might reduce the risk of anemia caused by too little iron in the body during pregnancy.
There is interest in using chlorella for a number of other purposes, but there isn't enough reliable information to say whether it might be helpful.
Likely ineffective Effectiveness definitions
Possibly ineffective Effectiveness definitions
Insufficient evidence Effectiveness definitions

Dosing & administration

Chlorella has most often been used by adults in doses of 3-10 grams by mouth daily for 2-3 months. Speak with a healthcare provider to find out what dose might be best for a specific condition.

Keep in mind that chlorella products can vary depending on the way the chlorella was cultivated, harvested, and processed. Dried chlorella can contain from 7% to 88% protein, 6% to 38% carbohydrates, and 7% to 75% fat.

Interactions with pharmaceuticals

Medications that increase sensitivity to sunlight (Photosensitizing drugs)

Interaction Rating=Moderate Be cautious with this combination.

Some medications might make the skin more sensitive to sunlight. Chlorella might also make the skin more sensitive to sunlight. Using these products together might increase the risk of sunburn, blistering, or rashes when the skin is exposed to sunlight. Be sure to wear sunblock and protective clothing when spending time in the sun.

Warfarin (Coumadin)

Interaction Rating=Moderate Be cautious with this combination.

Chlorella contains large amounts of vitamin K. Vitamin K is used by the body to help the blood clot. Warfarin is used to slow blood clotting. Chlorella might decrease the effects of warfarin. Be sure to have your blood checked regularly. The dose of your warfarin might need to be changed.

Interactions with herbs & supplements

Herbs that might increase sensitivity to sunlight: Chlorella might make the skin more sensitive to sunlight. Using it with other products that also make the skin more sensitive to the sun might increase the risk for sunburn and other side effects. Examples of supplements with this effect include bishop's weed, chlorophyll, khella, and St. John's wort.

Interactions with foods

There are no known interactions with foods.
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This monograph was last reviewed on 19/03/2022 00:14:21 and last updated on 18/05/2018 00:39:32. Monographs are reviewed and/or updated multiple times per month and at least once per year.
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