I tried many years ago for health benefits but could not tolerate the taste.
Below are possible side effects :
"
Spirolna Possible Side Effects
It’s absolutely critical to make sure that the quality and purity of the spirulina that you consume is of the highest standards. Particularly, like anything that comes from the sea, be certain to only purchase blue-green algae that is free from contamination. According to WebMD, contaminated spirulina can cause the following:
Liver damage
Stomach pain
Nausea
Vomiting
Weakness
Thirst
Rapid heartbeat
Shock, and even death
Also, some sources suggest that pregnant women and children should not consume algae. Contact your natural health care provider to confirm whether or not you should be supplementing with SpirolnaSpirulina"
Source.
http://draxe.com/spirulina-benefits/