Creatine Powder: This is a natural acid we produce in our body to accomodate the sudden need of energy.  Example would be flight of fight mode and lifting weights or needing to evaluate a dramatic situation for survival. 

Studies show that this sudden release of this acid improves brain power and reduces mental fatigue. 

Creatine is also found in common foods like salmon and beef. It all happens by drawing in water to the muscles, quickly, making them instantly larger.

Since creatine is stored mainly in fresh meat and some fish, (not vegetables) this is a great way to add it's benefits to our bodies if we are non meat eaters

Some recent studies have shown great promise for creatine use for those suffering from musclular dystrophy and other muscular diseases.  Also in neurological disorders and heart failure.

Adverse Side Effects: In healthy humans no side effects have been noted, however there is some controversy pending, like some dehydration with prolonged use.  Consult with your physician before using any supplement.