I'm not sure this is what you're looking for, but I have a couple of fics with John hallucinating because of drugs.
Adverse Reaction (http://wildcat88.livejournal.com/18777.html#cutid1) and Trial By Fire (http://community.livejournal.com/sga_flashfic/746632.html#cutid1)
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Date: 2008-05-06 10:10 pm (UTC)Adverse Reaction (http://wildcat88.livejournal.com/18777.html#cutid1) and Trial By Fire (http://community.livejournal.com/sga_flashfic/746632.html#cutid1)