@Lumos1992,
I believe that the people who abuse dextromethorphan get cough syrup that does not have other cold products in it. High doses of the
other cold products may have unpleasant or dangerous effects.
Note that dextromethorphan has PCP-like effects. People who use this family of drugs tend to go on violent crime sprees and get shot to death by police officers.
It is unlikely that people on this website have experience with this caliber of drug abuse. If they do, they certainly don't publicize it. Unless someone privately messages you in secret, it is safe to assume that no one here has such experience.
I only know a bit about it because it was Trayvon Martin's drug of choice and I participated in the George Zimmerman self defense threads.