Side Effects of Chlorella Supplements

According to the American Cancer Society, chlorella (sun chlorella, green algae) is a single-celled freshwater alga that has an abundance of chlorophyll. Chlorophyll gives leafy vegetables their green color. Chlorella is commonly used in Japan to treat a number of medical conditions. In the United States, sun chlorella is sold as a dietary supplement.

Supporters maintain it can eradicate some cancers, improve the immune system and encourage the healing of intestinal ulcers. Other touted uses include fighting off viral and bacterial infections, cleansing the liver and blood. The ACS says there is no scientific proof to verify these promoted effects. Sun chlorella may produce a number of side effects.

Side Effects

Some people who take sun chlorella may suffer from gastrointestinal problems including gas, abdominal pain, nausea, diarrhea and/or constipation. Additional side effects may include fatigue, irritability and increased sensitivity to sun exposure.

Allergic Reactions

Chlorella seems to be safe for people who are not allergic. An allergic response includes breaking out in skin hives or a rash, a swelling of the skin and possible chest pain. You may also have difficulty breathing and feel tightness in your chest or throat. If you have any of these symptoms, stop taking sun chlorella immediately.


There have not been any studies conducted in humans to determine whether sun chlorella causes negative side effects--or what, if any, effects may be associated with prolonged use.

The ACS cautions not to depend on chlorella to replace traditional medical treatments for serious health conditions such as cancer.

Take only the recommended dosage listed on the label. Be sure to tell your doctor if you have any existing medical conditions, such as high blood pressure or heart or blood vessel disease. Don't take sun chlorella if you are pregnant or breast feeding.

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