Is creatine a peptide?

No. Creatine (creatine monohydrate) is a naturally occurring compound made from three amino acids (glycine, arginine, methionine), but it is not a peptide — the amino acids are not linked in a peptide chain. Creatine is classified as a nitrogenous organic acid. It is one of the most extensively studied performance supplements with strong clinical safety and efficacy data.