What is Creatine

Creatine is an amino acid located mostly (95%) in your body's muscles as well as in the brain. Once consumed it is stored as phosphocreatine primarily in your muscles. Most people take creatine orally to improve athletic performance and muscle gain.

Other uses include improving brain disorders, congestive heart failure or  skin care.

Creatine can be produced from food, mainly meat. Vegetarians should probably supplement. 

Creatine stored water so people with kidney problems should consult their doctor. Also it promotes water based weight gains in first months of usage.