To the reader:

The problem with taking any kind of stimulant while drinking is that it can mask the effect of the alcohol. That means that you will probably feel more sober, and therefore is less likely not to drive, because "Hey, I'm almost sober." Another problem is that when the stimulant is wearing off, the alcohol is still in your body and you can go from "sober" to passing out in a matter of minutes.

And just a piece of advice: Don't drink and do drugs at the same time, just don't! So many accidents/overdoses on drugs happen because people combine stuff that really shouldn't be combined.