To my suprise, my psychiatrist diagnosed me with ADHD when I was 21. I was perscribed adderall for this. I don't really think I have ADHD, but I didn't mention this since I wanted the meds. I seldom take this anymore, as it makes me anxious. For me, weed is much better for studying. Partly this is cause I use it as a reward for finishing a chapter/assignment, etc. But I can definitely testify to the fact that it can help concentration to some degree. Definitely helps clear the mind of distractions that might disrupt study. That said, I work slower on pot (though more carefully), and It definitely impairs memory and other mental functions somewhat. I do all my important thinking while sober or almost so.