The prevention of an enzyme from binding to its intended substrate as a result of the presence of another molecule which can also attach to the enzyme's active site. The other molecule competes with the substrate for the active site, and the more of the other molecule there is, the slower the enzyme is at carrying out its intended purpose. This type of enzyme inhibition is reversible by increasing the amount of the enzyme's intended substrate. Compare noncompetitive inhibition.The term can also be generalized to apply to any other set of molecules which compete with and inhibit one another for the same site.