You can read about spirulina on various sites, such as here or on wikipedia.

Be careful to buy good quality organic spirulina, and don’t give spirulina to children without some very careful research and consulting experts. It’s not suitable for everyone.  You can buy it in health food shops or online (on Amazon for example, where you can read the reviews).  Some nutritionists have stated that you should always drink plenty of water when taking spirulina.

The first time I had spirulina, I drank a large tablespoon of it in a home-made energy drink and felt nauseous for a day or two – it could be I was de-toxing.  It can be strong stuff.  I am now reluctant to drink it straight, but am very happy with spirulina in a smaller dose so I’ve had no problem with Healthy Spirulina Energy Balls.