Pharmacology
Dextromethorphan's hallucinogenic and dissociative effects can be attributed largely to dextrorphan (DXO), a metabolite produced when dextromethorphan metabolizes within the body. Both dextrorphan and dextromethorphan are NMDA receptor antagonists, just like the dissociative hallucinogenic drugs ketamine and phencyclidine (PCP); however for that purpose, dextrorphan is more potent than dextromethorphan.
Just like all NMDA receptor antagonists, dextrorphan and dextromethorphan inhibit a neurotransmitter called glutamate from activating receptors in the brain. This can effectively slow or even shut down certain neural pathways, preventing areas of the brain from communicating with each other. This leaves the user feeling dissociated (disconnected) or potentially "out-of-body."
Dextromethorphan's euphoric effects have sometimes been attributed to the triggering of an increase in dopamine levels, since such an increase generally correlates to a pleasurable response to a drug, as is observed with some antidepressants and recreational drugs. However the effect of dextrorphan and dextromethorphan on dopamine levels is a disputed subject. Studies show that some NMDA receptor antagonists, like ketamine and PCP, do raise dopamine levels. Other studies show that dizocilpine, another NMDA receptor antagonist, has no effect on dopamine levels. Some findings even suggest that dextromethorphan actually counters the dopamine increase caused by morphine. Due to these conflicting results, the actual effect of dextromethorphan on dopamine levels remain undetermind.
Read more about this topic: Recreational Use Of Dextromethorphan