Creatine is an amino acid located mostly in your body's muscles, as well as in the brain. Though it can be made synthetically, most people get creatine through seafood and red meat. The body's liver, pancreas and kidneys also make creatine.
Your body converts creatine to phosphocreatine and stores it in your muscles, where it's used for energy. As a result, people take creatine orally to improve athletic performance and increase muscle mass.