That question has nothing in common with:
except for the cough syrup.
And the answer to your question is “it depends, but it’s generally not a good idea”. Time to fight some ignorance, I guess. Mods, I hope I don’t cross a line here. Apologies in advance if I do. Alright then, DXM works thusly: (I’ll use the dosage levels for when I did it; I weighed 175 at the time)
There are four (ETA: numbered/vaguely sane) dosage levels, called “plateaus” in the tripper parlance, which are mostly quite different experiences. A trip lasts 6-8 hours, with the “peak” occurring somewhere between smack-in-the-middle and maybe 2/3 of the way through the duration. In each plateau, you can feel the “peak” effects of each plateau before it, in turn, before you finally reach the peak of the plateau you dosed on. After that, the effect gradually fades, getting less and less intense until you don’t feel it at all. Withdrawal is pretty unlikely except in the saddest cases of addiction; when you come down, you tend to feel like you’ve completed a journey and it’s time to kick back and relax. (You might have been physically relaxed during the trip, but mentally, ‘loop-de-loops in the astral plane’ describes it fairly well.)
Each plateau is triggered by a range of doses that depends on your weight. As I said above, I’ll list the doses I took, and I weighed 175 lbs then. And I’m only listing the specific doses I found worked well for me, not the dosage range, which can be more fluid.
First Plateau (150 mg)
Come-up: Slightly buzzed, somewhat like being drunk and wired on a low dose of speed at the same time. Music is an incredible experience; not so much trippy as much as it is just better. It’s like the difference between listening to a CD and going to Copley Symphony Hall. Robo-walking, as described by Drain Bead. Driving is generally fine, though it’s not wise to overdo it. This is the “party dose”, if there is such a thing for DXM. (I found it was best enjoyed with one close friend, or by oneself; never would have dreamed of taking it at a party at all. It’s just not a social drug.)
Peak: Basically a more intense version of the come-up. Typically you’ll have some mildly psychedelic closed-eye visuals (CEV); that is, if you turn on some music, lay down and close your eyes you’ll see some trippy patterns that generally don’t amount to much of anything. No open-eye visuals (OEV), although when your eyes are open there is a sense that the world is a little shakier; reading at a distance may be imprecise, which is why it’s not a particularly good idea to drive. If you have to drive, though, it’s generally not as bad as driving drunk, but some first-plateau peaks are strong enough to make it a pretty bad idea.
Second Plateau (300 mg)
Come-up: First the slight buzz of the First Plateau; then, the musical effects and the robo-walking; then, an experience roughly equivalent to the First Plateau peak. CEVs gradually get more and more intense as you lead up to the peak. If you must drive, it’s not a huge huge deal early in the Second Plateau trip, but the less (and the earlier) the better. Music then turns from “awesome” to “awesome and trippy”–I loved to turn on the radio and just zone out, lying down with my eyes closed; at this point you can see more well-defined things. For example, a close friend and I both saw a “Pink Man” on most of our Second Plateau trips; just an image of a man in silhouette who was everything it ever meant to be pink. Just the complete essence and archetype of that color. Against a pinkish red background, of course. He swayed swiftly to the music, and he never talked but he was a fascinating study. MMV. I also saw some more serious visions, like one time when it suddenly occurred to me that so much of the things our society is built on are a coordinated facade. It was much more detailed than that, and involved flying through a fake city and staring at the storefronts for a while, with a bunch of other visual cues; the “truth” I found was more of an emotional resonance than a string of words.
Peak: This is where the “dissociative” part comes in. CEVs often become so intense that the tripper leaves his/her own body and may become completely separated from the outside world–not dangerous in and of itself, but it makes it a really bad idea to drive once you’re more than two or three hours into the trip, until you come back down. OEVs are prevalent too; but rather than “modifying” the things you really see to make them more trippy, OEVs at this point tend to take you away from the real world entirely, like CEVs. Again, not dangerous in and of itself, as long as the tripper is somewhere safe at this point where s/he won’t be unduly bothered by other people or threatened by animals (hence why DXM is generally not a camping drug, IMO). Generally CEVs/OEVs at this point have crossed the line from “visuals” into “complete psychedelic experience”; a truth about the tripper is usually revealed and analyzed within his/her mind’s eye.
Personally, I used to take a second plateau dose every week or two, for maybe six months or so, give or take a few. Almost every single time, at the peak I would see an “action replay” of something I had done or said that week, and then in splitscreen, I would see a “dramatization” of how I could have done/said it better. Fairly powerful stuff, but not earth-shattering like the realizations that other psychedelics can lay upon you. Some people report that second plateau trips helped them kick bad habits; that was certainly my experience, and I like to think I came out a better person. OTOH, I wouldn’t be surprised if the second plateau were the most addictive. I’m not really an addictive personality, though, and the science is unfortunately lacking on that level of detail, so I wouldn’t know.
Third Plateau (600 mg)
This is the furthest up I ever went. I did it once. It was mind-blowing, and I felt like I got all I could have gotten out of the Third Plateau and, for the most part, out of DXM in general. I had a few Second Plateau trips after that, and a handful of First Plateau trips as well, but for the most part my third pleateau trip ended DXM for me.
Come-up: A little robowalking, a little of that Copley Hall stuff, then almost straight into the trippy stuff. There is no reason to drive on this dosage, period. It’s just a bad idea. One or two Second-Plateau-peak type psychedelic revelations may occur, and OEVs and CEVs are strong.
Peak: Simply one of the most mind-blowing things I have ever experienced. It just cannot be described. It’s like visiting an alien planet. Your entire frame of reference for everything is shaken up, put down briefly, then picked back up and thrown across the room. You may see incredibly moving images, including “mind pictures” from your childhood. It’s emotionally and psychologically taxing–this peak is a lot of work. But you come out of it with a completely new understanding of life in general. And, oh yeah, palpable dehydration. It’s a really good idea to drink a lot–a lot–of water throughout. And it’s a bad idea to be anywhere where well-meaning friends/family/roommates/general public will see you, because you’ll look like you’re completely gone from this world. And really, for an hour or two, you will be. I never felt the need to revisit that, personally. I doubt that I ever will either.
The Fourth Plateau is even more earth-shattering at its peak, as you might imagine. I won’t cover it in any detail, really, since I don’t have any personal experience, but here is some experiential info.
Plateau Sigma is a strange beast; it involves keeping the dosage level in your body constant for a while, and, again, reportedly takes you to a whole 'nother level. Which most people find frightening and incredibly unpleasant.
The page I linked to has more information about the other plateaus, and a bevy of other DXM information in there too, for the bored and curious.
This is not intended as an endorsement of the drug.
Generally yes IIUC, but it probably varies by state.