This review is focused on creatine (CR) (methyl guanidine acetic acid) and its application in the form of a dietary supplement. It has been especially utilized by athletes, but its pronounced therapeutic potential is also discussed in the present article. It is supposed that human body uses CR for the formation of creatine phosphate (PCr), which is necessary for muscular work as a source of energy. The effects of supplemented CR on dynamics of methionine cycle and other related metabolic pathways have not been fully explained yet. The review is focused on the description of affects caused by its application on human body and metabolism. Already the application of small amounts of CR rapidly increases levels of thiodiglycolic acid (TDGA) in urine after its supplementation, which phenomenon can serve as a sensitive marker of disturbance in metabolic pathways of 2C units and of thiolic compounds. Strong differences between initial and terminal TDGA levels in urine indicate that CR disturbed the equilibria of redox processes, catalyzed by folates and vitamin B-12. Some theories for explanation of these effects are described in this manuscript. Nevertheless, similarly as in other metabolic studies, the results are significantly affected by the probands' individual responses, which reflect their individual genetic makeup. The various methods such as voltammetric (generally electrochemical), chromatographic, mass spectrometric, enzymatic etc., which have been most frequently utilized for determination of discussed compounds in common laboratories, have been reported.