Short term memory loss (even when I'm not intoxicated.. literally I'll forget what I'm talking about in mid-sentence and shit. I have no idea what I ate or did yesterday and I didn't take any drugs.)
Apathy, self-induced ADD, irritability, past addictions, now dependencies, insomnia, OCD thoughts, the list goes on...
I noticed this a lot with my friends who all got into drugs. A lot of them also have a difficult time pronouncing words, no matter how many times they're corrected.