In general, oral supplementation of creatine increases muscle creatine content by 15%–20%, which is more than a 20 millimolar (mM) increase. Individuals who get a response of this magnitude are considered creatine responders.[1][2][3][4] Creatine non-responders are individuals whose muscle creatine content increases by less than 10 mM after prolonged supplementation with creatine,[5] while creatine quasi-responders are individuals whose muscle creatine content increases by 10–20 mM.[5]
Non-response to supplemental creatine is thought to explain instances in which not all participants benefit from supplementing with creatine in trials.[6]