A friend of mine dropped out of a full four year college scholarship and quit his job after prolonged use of DXM. During the winter he managed to do cough medicine nearly every day perhaps due to seasonal depression. He then fell into a state of delerium reporting that the "DXM gods" had manifested inside of him and that he was in another world even without cough medicine. This lead him to a life-changing trademark epiphany- that "the past doesn't matter anymore". Here we are a year later and he still has no job and visits the DXM gods several times a week.

The substance doesn't matter, it is the person using it.
Mild schizophrenia is no more a mental illness than christianity. Besides, we all see things and hear voices telling us to kill at one point or other am I right?
http://alcoholism.about.com/cs/pot/f/mjp_faq18.htm