Creatine derivatives and compositions containing a bioactive form of creatine. The new chemical entity comprises an acetyl creatine, N-acyl creatines, N,N-diacyl creatines or any N-acetyl creatine species with enhanced solubility and bioavailability. Also provided by this invention are various methods for providing several beneficial effects that comprise administering compositions comprising N-acetyl creatine, N-acyl creatines, N,N-diacyl creatines or any N-acetyl creatine species to a mammalian subject, either chronically or acutely.