As far as I know, therapists aren't supposed to officially diagnose anything. Basically it seems that if they can prescribe, they can diagnose. If they aren't allowed to prescribe, they aren't supposed to make anything more than a tentative diagnosis. I think it has to do with the training that they received.

Ironically, GP's can diagnose even though they would often know less about the conditions and meds than therapists. I had GP-based diagnosis in the past, and no one in the psych field will believe those diagnoses.

I heard yesterday (from my T) that the surest way to evaluate ADHD is to prescribe meds. If they make you all hopped-up, then you don't need 'em and you don't have ADHD. If they make you focused, then bingo! The catch with that is that people who have DEA approval for prescribing controlled substances are very, very careful about who gets what meds because it can be a big, big mess (for them) if they're not.

Another distinguishing detail is the the mental health nurse practitioners can generally prescribe controlled substances (DEA schedule 2) but that's not true of all NP's. When I was getting my ADHD prescription through the university health center, I had to specify that I needed an ADHD refill when I called for an appointment so that they would set me up with the right person rather than someone who can't write that rx.