As a medicine, it can definitely be abused. It wont kill brain cells, but it can temporary shock them. You are not necessarily at your finest when you are blitzed out of your mind.
I think that only tiny amounts of sativa in the AM, and maybe some heavier Indica if you have pain or before sleep....thats about the extent of it for me. I dont get 'baked' when I have stuff to do.
Yes, It can definitely be over used to your detriment, but not in the BS ways that the propaganda campaigns tell you that it will.