An inhibitor is something that slows down or suppresses a reaction.
An hibitors is a substance that is added to another product, solution, solid etc. to prevent or slow down reactions or changes
Drugs that block catechol-o-methyl transferase, an enzyme that breaks down dopamine
A serotonin reuptake inhibitor is one example. There are several of these (including Lesapro, Celexa, Zoloft, Paxil and Prozac).
Dopamine or serotonin antagonist e.g. risperidone or amisulpride.