I think that was a very important question the earlier poster (I can't remember your screen name!) raised about whether or not the culprit may not be Accutane. The psychosis reaction to that drug has been well reported, particularly in young men. That really is an important thing to relate to your doctor.

Accutane is a strong and scary drug. Far scarier than grass, I feel. And far more likely to be what's causing those symptoms you're having, in my opinion.