It fills the muscles with water, that is where the creatine deaths come from. And muscle "gain". They get dehydrated.
Nick....it's in your steak.
http://en.wikipedia.org/wiki/Creatine
Supplementation can be dangerous if you have a pre-existing kidney condition.....but that's about it as far as serious concerns go. :idunno:
....and anyone who knows the substance knows that it doesn't really grow muscle :nono: ....the purpose of supplementation is to make your muscles more efficient at energy consumption so you can work harder to achieve greater gains.