Dennis -

This is an easy one. Check out what the DEA has to say about the active ingredient in your cough medicine:

Dextromethorphan (DXM) (d-3-methoxy-N-methyl-morphinan) is the dextro isomer of levomethorphan, a semisynthetic morphine derivative. Although structurally similar to other narcotics, DXM does not act as a mu receptor opioid (e.g. morphine, heroin). DXM and its metabolite, dextrorphan, act as potent blockers of the N-methyl -d-aspartate (NMDA) receptor. At high doses, the pharmacology of DXM is similar to the controlled substances phencyclidine (PCP) and ketamine that also antagonize the NMDA receptor. [Emphasis added.]

http://www.deadiversion.usdoj.gov/dr...m/dextro_m.htm

Mike