The two are frequently interlinked, though, which makes things challenging. A large number of the people we treat are dealing with, for example, schizophrenia and meth addiction. I didn't mean a dx should be based entirely on that, just that I've personally witnessed some patterns working in the field. It is difficult to sort out what's what, though, because street drugs and alcohol generally tend to affect people differently. Another example, though also anecdotal, my sister actually somehow manages her bipolar disorder with weed (???). Weed makes me hallucinate and I can't stand it.

Oh - to add a little more personal experience I probably shouldn't - I am a former heroin addict. I currently take a lot of (prescribed) benzos. I tend to run manic about 80% of the time. The drugs I chose were almost always pure downers, because mania is exhausting and I constantly felt like bursting out of my skin. Other things usually just made me psychotic.