A buddy who does a fair bit of DXM
has tried coricidin
before apparently, and apparently he finds it different than DXM-only formulations. For one, the trip itself is more sedated and 'fuzzy' than DXM-only; one would think this is from the anti-histamine action in addition to DXM. They definitely seemed more out of it compared to just DXM (i.e. less motor control, more pronounced robo-walk, general 'stoned' look), but they also said they didn't like it as much as just DXM since the psychedellic aspects of the trip were less pronounced (this was his main reason for doing DXM, so it kinda defeats the point for him).
Positively, he had no itch on the come up (rare for him anyways, but worth mentioning) and a better afterglow once the trip was over. He also said he tripped a little longer too, but this may have been subjective (easy for the minutes to drag with DXM).
As noted above, this is a potentially lethal combination if used in excess or if you happen to be unlucky enough to be susceptible to this combination (rare, but its happened). Would recommend one sticks to the label on this, at the very least don't go over 8 pills. There are safer ways to modify the trip such as cannabis
(careful now, I've heard this can have some extreme results) or if you're trying to combat the nausea or itch go with some dyphenhydramine (start small, it may affect you differently).
All in all, its not worth it for the risk.