I have two questions, though the first ties into the second.

First: PCP, Ketamine, and DXM all work because they're NMDA antagonists, but supposedly they all have different effects. How do chemicals that work on the same receptor have different effects?

Second: It's recently been stated (the DL-Phenylalanine thread) that Magnesium is a NMDA antagonist. Is it possible that in higher doses it would produce an effects profile similar to the three mentioned above? Also, the first thing that comes to mind when you think of high doses of magnesium is diarrhea, but another conclusion of the DLPA thread is that Mg can be taken sublingually to prevent said symptoms.