Both inhibitors decrease the rate of reaction for an enzyme controlled reaction. A competitive inhibitor has a similar shape to the substrate, therefore, its shape is complementary to the active site of the enzyme . The competitive inhibitor can then bind to the active site, blocking the substrate from binding to the enzyme. This means hydrolysis of the substrate cannot occur and so the rate of reaction decreases.A non-competitive inhibitor does not bind to the active site of an enzyme. Instead, it binds to another area of the enzyme called the allosteric site. By binding to the allosteric site, it changes the specific tertiary structure of the active site and means the active site is no longer complementary to the substrate, so hydrolysis cannot occur.