Newly developed forms of creatine are often claimed to exhibit improved bioavailability and efficacy. They are of great interest for sports nutrition and therapeutic uses. However, for most newer creatine forms stability after ingestion under physiological conditions is insufficiently documented, relevant data are inconsistent or even missing. Therefore, we developed a controlled simulated digestion system for testing different creatine derivatives in specific simulated parts of the human digestive system. All derivatives showed high stability with negligible formation of creatinine.