Blue-green algae are a group of bacteria. They can be used as a source of protein, but contain no more protein than meat or milk.

Blue-green algae produce blue-green colored pigments and are high in protein, iron, and other minerals. They grow in saltwater and some large freshwater lakes. They have been used for food for several centuries in Mexico and some African countries. In the US, they’ve been sold in supplements since the late 1970s.

People use blue-green algae for treating high blood pressure and as a protein supplement. It’s also used for high levels of cholesterol or other fats (lipids) in the blood, diabetes, obesity, and many other conditions. But there is no good scientific evidence to support these other uses.

Some blue-green algae products are grown under controlled conditions. Others are grown in a natural setting, where they’re more likely to be contaminated. Only use products that have been tested and are free of contaminants such as heavy metals, liver toxins called microcystins, and harmful bacteria. Don’t confuse blue-green algae with other algaes, like Ascophyllum nodosum, Ecklonia cava, Fucus Vesiculosis, or Laminaria.

Natural Medicines Comprehensive Database 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.

The effectiveness ratings for BLUE-GREEN ALGAE are as follows:

Possibly effective for…

• High blood pressure. Taking blue-green algae by mouth seems to reduce blood pressure in some people with high blood pressure.

There is interest in using blue-green algae for a number of other purposes, but there isn’t enough reliable information to say whether it might be helpful.

When taken by mouth: Blue-green algae products that are free of contaminants are possibly safe for most people when used short-term. Doses up to 19 grams daily have been used safely for up to 2 months. Lower doses of 10 grams daily have been used safely for up to 6 months. Side effects are typically mild and may include nausea, vomiting, diarrhea, headache, and dizziness.

But blue-green algae products that are contaminated are possibly unsafe. Contaminated blue-green algae can cause liver damage, vomiting, weakness, rapid heartbeat, shock, and death. Don’t use any blue-green algae product that hasn’t been tested and found to be free of microcystins and other contaminants.

Special precautions & warnings:

Pregnancy and breast-feeding: There isn’t enough information available to know if it is safe to use blue-green algae when pregnant or breast-feeding. Contaminated blue-green algae products contain harmful toxins that might be transferred to an infant during pregnancy or through breast milk. Stay on the safe side and avoid use.

Children: Blue-green algae are possibly unsafe for children. Children are more sensitive to contaminated blue-green algae products than adults.

Auto-immune diseases such as multiple sclerosis (MS), lupus (systemic lupus erythematosus, SLE), rheumatoid arthritis (RA), pemphigus vulgaris (a skin condition), and others: Blue-green algae might cause the immune system to become more active, and this could increase the symptoms of auto-immune diseases. If you have one of these conditions, it’s best to avoid using blue-green algae.

Surgery: Blue-green algae might lower blood sugar levels. There is some concern that it might interfere with blood sugar control during and after surgery. Stop using blue-green algae at least 2 weeks before a scheduled surgery.

Moderate

Be cautious with this combination.

Medications for diabetes (Antidiabetes drugs)

Blue-green algae might lower blood sugar levels. Taking blue-green algae along with diabetes medications might cause blood sugar to drop too low. Monitor your blood sugar closely.

Medications that decrease the immune system (Immunosuppressants)

Blue-green algae can increase the activity of the immune system. Some medications, such as those used after a transplant, decrease the activity of the immune system. Taking blue-green algae along with these medications might decrease the effects of these medications.

Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)

Blue-green algae might slow blood clotting. Taking blue-green algae along with medications that also slow blood clotting might increase the risk of bruising and bleeding.

Herbs and supplements that might lower blood sugar

Blue-green algae might lower blood sugar. Taking it with other supplements with similar effects might lower blood sugar too much. Examples of supplements with this effect include aloe, bitter melon, cassia cinnamon, chromium, and prickly pear cactus.

Herbs and supplements that might slow blood clotting

Blue-green algae might slow blood clotting and increase the risk of bleeding. Taking it with other supplements with similar effects might increase the risk of bleeding in some people. Examples of supplements with this effect include garlic, ginger, ginkgo, nattokinase, and Panax ginseng.

Iron

Blue-green algae can decrease the amount of iron the body can absorb. Taking blue-green algae with iron supplements might decrease the effects of the iron supplement.

Keep in mind that taking blue-green algae can decrease the amount of iron the body can absorb from food and supplements.

Blue-green algae has most often been used by adults in doses of 1-10 grams by mouth daily for up to 6 months. Only use products that have been tested and are free of contaminants such as heavy metals, liver toxins called microcystins, and harmful bacteria. Speak with a healthcare provider to find out what product and dose might be best for a specific condition.

AFA, Algae, Algas Verdiazul, Algues Bleu-Vert, Algues Bleu-Vert du Lac Klamath, Anabaena, Aphanizomenon flos-aquae, Arthrospira fusiformis, Arthrospira maxima, Arthrospira platensis, BGA, Blue Green Algae, Blue-Green Micro-Algae, Cyanobacteria, Cyanobactérie, Cyanophycée, Dihe, Espirulina, Hawaiian Spirulina, Klamath, Klamath Lake Algae, Lyngbya wollei, Microcystis aeruginosa and other Microcystis species, Nostoc ellipsosporum, Spirulina Blue-Green Algae, Spirulina fusiformis, Spirulina maxima, Spirulina platensis, Spiruline, Spiruline d’Hawaii, Tecuitlatl.

To learn more about how this article was written, please see the Natural Medicines Comprehensive Database methodology.

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