Creatine is one of the most popular dietary supplements worldwide among not only elite athletes but also among adult recreational, child and adolescent athletes, and the elderly (1). Creatine is not on the World Anti-Doping Agency’s 2017 prohibited substances list (2).

Creatine, or methylguanidine acetic acid, is made in the liver from the amino acids arginine, glycine and methionine (3). Once synthesized, creatine leaves the liver and travels to enter the muscle cell via