Good, bad, as a moral issue it doesn't matter...some advice from someone who long ago when I was young and niave did I like to pretend that your theory would work. Some advice, If you are actually serious. By all means, do what you want to relax or expand yoru mind in your spare time, your not hurting anyone, except your lung tissue and short term memory. As for doing it before the highly important MCAT!...come on, it will NOT increase memory recall, and certainly will decrease optimum functioning of your brain, which you will want to be working with synapse firing instantaneously, not delayed and hindered
. Perhaps it could be argued that recreational use may allow a person to think more deeply and detailed, perhaps even conceptually visualize a bit better. But that is when you have a lot, lot, lot of time on your hands to freely ponder. Not a good idea for this test.
If your implying instead, that it is to relieve test anxiety, I'm sure there are better, smarter, non-chemically induced strategies, that will not have the side effect of hindering your brain functioning for this type of test.