What is the difference between a competitive and a non competitive inhibitor?

Competitive inhibitors have a molecular shape similar to the substrate therefore compete with the substrate for the active site on the enzyme. If the concentration of substrate increases, the effect of the inhibitor decreases and visa versa. A non competitive inhibitor attaches themselves to the enzyme but not on the active site. The binding of the non competitive inhibitor to the enzyme alters the shape of the active site so that it is no longer complementary to the substrate. An increase/decrease of the inhibitor will have no effect on the rate of reaction.