I don't feel like reading this thread but I was actually talking about this today at work lol. You can buy the robotussin with JUST DXM as the active ingredient in it, so there's no additives really other than the stuff that makes up the unpleasant and viscous taste of cough syrup.
It's not gonna kill ya if you don't drink a shitload, but it doesn't matter because the trip is the worst ever. I did the stuff a few times at a time when erowid.org was my homepage and I was trying to just do whatever drugs I could find out of an experimental lust for assaulting my consciousness that would nowadays make me loose my shit (ah the beauty of life before cynicism).
Anyways, all the times that I did it I basically had vague peripheral hallucinations of dark creatures nearby and everything made me depressed. Did it with some friends in college and they all said the same thing. Bottom line is, yeah it trips you out, but who wants to go out of their way to ingest a nauseating substance that gives you a negative downer trip?!?
For you kids out there: If you are dying to trip, wait until you get a connect with some mushrooms or just smoke some weed, the fact that it's cheap and available doesn't invalidate the fact that its the worst altered consciousness experience you can punch into your brain.