Uppers and Downers: Either way blood flows?

[Politicalchalk]

Swim originally was going to post this is "Drug Combinations," but after viewing some of the posts there, my question seems more appropriate here.

For conversational purposes, the drugs in question shall be phentremine and lorazepam, however, this could be extended to general uppers and downers.

So, say takes lorazepam, and an hour later takes some phentremine. Or even perhaps taking them at the same time. In the nervous system, who wins? Will the phet kill ALL the benzo properties, SOME of the benzo properties, will they cancel out?

And what of general timing issues? Does it matter which is taken first if taken reasonably close together (say 15-30mins)?

The base question: is it possible to enjoy the effects of both (orally) without them canceling each other out?