DXM and its metabolite, dextrorphan (DXO), produce different sets of
effects. Normally, DXM is converted mostly or entirely into DXO, but with
recreational doses, the conversion enzyme (P450-2D6) may saturate, leaving
a mixture of DXM and DXO. Furthermore, another of DXM's metabolites -
3-methoxymorphinan - can also block this enzyme, so that taking divided
doses leads to more DXM and less DXO than taking a combined dose of the
same amount.
DXM's effects are in some ways much more subtle than DXO's. Whereas DXO
produces a heavy "stoning" or intoxicating effect, DXM by itself is only
lightly intoxicating. DXM, however, can alter the thought processes,
leading to highly abnormal, psychosis-like mental states. It is possible
that DXM, via sigma activation, may induce a mental state similar to that
of schizophrenia. Whether or not this is fun to you is, of course, up to
you.