A non competitive enzyme binds to the enzyme but not at the active site. This creates an enzyme inhibitor complex. The binding of the inhibitor to the enzyme influences the chemical bonds (for example hydrogen bonds) within the enzyme, this changes the tertiary structure of the enzyme. As a result the shape of the active site is changed so that the substrate is no longer a complementary shape to the active site. Therefore fewer enzyme substrate complexes are formed per a second and so fewer reactions take place per a second. This means the rate of the reaction decreases.