Dextromethorphan is used in nearly every brand of
cough syrup- i.e. Benelyn DM and the like. Like all cough supressing drugs (
codeine,
heroin, etc), DM is a mind altering drug. If one were to drink half a bottle of the stuff (not easy), one would be well on their way to an interesting
psychedelic experience.
But first, there is some unpleasantness. You first have to suffer through half an hour of strong nausea. DM acts as a purgative, loosening up your bowels and generally causing intestinal nastiness. Puking and nasty farting are par for the course.
But about 45 minutes into things all this becomes irrelevant. Your body begins to feel strange and alien. All the movements which previously seemed so natural are suddenly revealed as mere habit. Fluid and insectlike modes of motion seem much more interesting and efficient. Time stretches and sounds become altered. In dark settings visual hallucinations may begin - melting textures seem particularly common. At higher dosages true 'vision' style hallucination may begin.
The hangover is not physically awful, but more like a weakened version of the state itself. Avoid coffee, nicotine, and marijuana if you wish to avoid intense flashbacks. You may feel spacey and somewhat emotionally disassociated from your surroundings.
DM, like all disassociatives such as ketamine, PCP, and large doses of alcohol, can cause brain damage if used habitually. It can also be physically addictive. It is often mixed with guafisenine and acetimenophen, which respectively cause intense puking and painful bloody death if you overdose on them. If you feel the urge to experiment, for god's sake do some proper research to avoid these unpleasant consequences.