Well I think you would only have lesions if it actually were ms or bt, but don't quote me on that. As far as seeing the effects, studies show a slight shrinkage for those who are long term users. As far as what would constitute as a long term user, I'm not too sure. Why are you worried about this? Are you still living with parents and afraid they might find out? Or are you afraid if it does make the brain look different that the doctor might misinterpret the MRI for something that is an illness as opposed to something caused by drug use?