Riemann Zeta...you said..."The two chemicals should actually antagonize each other--one is a DA and 5-HT releaser, the other is a DA/SERT reuptake blocker. Curious."
But in fact...they are BOTH DA/SERT reuptake inhibitors...which would only be antagonistic if the reuptake transporters are saturated.
if what you said were the case...where one was a releaser and one was a reuptake blocker, it would result in potentiation...sometimes referred to as synergism...which is the ability of one drug to potentiate the effects of another. this would certainly not be antagonism.
also...cocaine binds very tightly to sodium channels...which is how it produces local anasthesia (think about the use of novocaine, zilocaine, lidocaine, or carbocaine to numb a very specific part of the body)...and if I remember from my studies well enough, this action at sodium channels has cardiovascular consequences.