Creatine: A compound the body synthesizes (makes) and then utilizes to store energy. The storage of energy occurs when phosphate molecules are attached to creatine to create creatine phosphate. Creatine phosphate is capable of donating phosphate to ADP in order to make ATP. ATP can then be converted into ADP with release of energy.
Creatine is sold as a dietary supplement and is used by athletes as a "legal steroid" to increase muscle bulk. There has been some concern about the long-term safety of creatine, particularly as to whether it may cause digestive, muscular and cardiovascular problems and possibly raise the risk of cancer.