There is a song about getting high off this called "Special K" by Placebo. It doesn't have anything to do with it, but I loved this song as a teenager not realizing what it was referring to.
This drug would be easy to abuse. If one is enough to reduce suicidal thoughts I would probably prescribe like 3-4 at a time and tell the patient to take one every 3/4 days in adjacent to something like lamital to give the other medication enough time to work. I think it works so well because you're essentially getting high and the high lasts a few days. I read the comments on Youtube and it said getting high on dxm (which is in most cough syrup) is almost the same.
http://en.wikipedia.org/wiki/Ketamine
The wiki is pretty useful, but there is a lot of jargon in it.