A catalyst or an Enzyme activator, in contrast, is a substance that increases the rate of a chemical reaction.
E.g., if a compound is so similar to (one of) the reactants that it can bind to the active site of a catalyst but does not undergo a catalytic reaction then that catalyst molecule cannot perform its job because the active site is occupied.
When the inhibitor is released, the catalyst is again available for reaction.
Index inhibitors or simplified as inhibitor predictably inhibit metabolism via a given pathway and are commonly used in prospective clinical drug-drug interaction studies.
[3] Inhibitors of CYP can be classified by their potency, such as: