antagonism
situation in which the response to one drug is decreased in the presence of another drug
synergism
when two drugs together produce a greater effect than either drug produces (involves both potentiation and addiction)
pharmacological antagonist
is a drug that has a definite affinity for a receptor but has little or no efficacy after being bound to it.
competitive antagonism
if the agonist is capable of dissociating from the receptor
noncompetitive antagonism
is incapable of being dissociated or displaced from the receptor.