I/E introverted / extroverted
N/S intuition / sensing
T/F thinking / feeling
P/J perceiving / judging
before you speculate, get the exact meanings of these words for this particular personality test:
http://en.wikipedia.org/wiki/Myers-briggs#Concepts
I think that psychedelics tend to pull one from (E) to (I), he can't help but dive in when so many amazing aspects of his mind are illuminated. softening the ego, there is not much of a pre-built framework with which to judge actions, and of course the user is much more 'in the moment' so psychedelics would also pull one from (J) to (P). thoughts get much more abstract, what's in front of you may or may not be real. this is obviously a pull from (S) to (N) [sensing individuals prefer tangible data, iNtuition people prefer a theoretical abstract approach]. and finally, on psychedelics you are pulled from (F) to (T) because as you ego is softened you approach matters less from the 'inside'... your viewpoint is less influenced by all that junk in your mind.
in sum it seems that psychedelics are 'INTP' drugs, which would explain why in the personality-type and drug use thread, every single INTP except one (and there were tons) listed psychedelics as one of their favorites
GABA depressants (alcohol, benzos) tend to increase primitive emotion and decrease 'cognitive executive functioning' so perhaps from (T) to (F). they tend to make people more responsive to external stimuli, especially emotionally, and increase interpersonal interaction (sometimes in a good way, sometimes in a bad way), so also GABA depressants pull one from (I) to (E)
dopa/nora stimulants tend to also orient one towards his senses/environment. (I) to (E). noradrenaline is the fight/flight guy, and one is on high alert on stims, so i would expect a shift from (N) to (S) as the distressed nervous system gets concerned with the very tangible here-now issues
opioids dont seem to me to cause changes in personality type