competitive inhibitors prevent the formation of the enzymes- substrate (lock and key) complexes. They have similar shape to the substrate and hence compete with enzyme. This may be permanent or temporary

Enzyme reactions happen when the chemicals involved fit into the active site of the enzyme, this lowers the activation energy and the reaction happens. Enzyme driven reactions can be slowed or stopped by 'Competitive Inhibition' this is where a similar shaped chemical to the reactant fits into the active site and blocks it so the enzyme stops working.

Competitive inhibition is when an inhibitor has a similar molecular shape to the substrate. The inhibitor occupies the active site of the enzyme preventing the substrate from occupying it, so there forms an enzyme-inhibitor complex rather than an enzyme-substrate complex.

Competitive inhibition occurs when a molecule that preferencially binds to the same receptor as our target, is used to inhibit the effcet of the target by competing for binding to the receptor.