Dextrorphan (abbreviated
DXO) is a
dissociative anaesthetic used to block
NMDA receptors. It may be administered following
stroke to reduce metabolism and prevent
ischemic brain damage. It is also used in to detect
PCP receptors.
Non-medical drug users will encounter DXO as the primary
human metabolite of
dextromethorphan, or
DXM. It is created when the liver enzyme
cytochrome P450 (also called
CYP2D6 or
debrisoquine 4-hydroxylase) removes the methyl group at position 6 of the DXM molecule.
The quantities of DXM found in a regular
dose of cough medication (~15mg) evidently do not produce active quantities of DXO. However, when DXM is consumed in
recreational or
psychedelic doses (100mg and up), large amounts of DXO are also created. DXO has
dissociative and
tranquilizing effects, which some liken to those of
marijuana. These effects are thought to soften some of the more bizarre and intense effects of DXM, and indeed people who have low levels of cytochrome P450 tend to have more disturbing (and longer) trips.
The amount of DXO relative to DXM can be decreased by dividing one's dose (because another DXM metabolite, 3-methoxymorphinan, blocks cytochrome P450), or by injecting DXM subcutaneously.
All information except the first paragraph extracted from William White's DXM FAQ, the most impressive piece of lay scholarship I've ever seen.