Unless you consider DXM an opiate my closest experiance with an opiate is codeine. (My dentist also gave me something he said was 100 times more powerful than morphine, but the next thing i knew i was looking at my dad with gause in my mouth, so if any questions i asked about it were answered, i don't know.)
And codeine just decreases my sensativity to pain a little(i've experimented by hitting myself on the leg with my fist as hard as i can while under no influence, and while under the influence. I've also experimented with other OTC pain killers.) What it does, that is interesting, is it guartentee's lucid dreaming. During the weeks following my wisdom teeth extraction I screwed more women in my dreams than during the last 3 years.