Creatine is a molecule that is produced in the body from the amino acids arginine, glycine, and methionine, which is naturally produced by the body. Creatine is involved in making energy for muscles. About 95% of it is found in skeletal muscle. Creatine monohydrate is among the safest and most well-researched forms of creatine supplements. It’s also widely available and generally the most cost-effective option.