Creatine is an amino acid produced naturally by the liver and kidneys and stored in muscles.
Athletes take creatine supplements to gain extra energy, train longer and harder - and bulk up.
The supplement is popular among pro and college athletes in the United States, where it is considered a legal alternative to steroids. The U.S. Food and Drug Administration lists it as a food supplement and allows it to be sold with no more restrictions than those on vitamins. Creatine is not listed as a banned substance by the International Olympic Committee, but its sale is illegal in France. High-profile athletes who have admitted to using creatine include the French tennis player Mary Pierce and U.S. baseball star Mark McGwire. The document urged sports governing bodies to consider listing creatine as a banned substance.