it slows all of the brain waves. has to do with alertness/readiness. (for example, the slowest is 'delta' which is when you're sleeping, or in a coma.) we would show people what their scan looked like compared to what it should look like and that sometimes motivated people to stop. so we'd take another to look for progress.
to go back to normal depends on age and how long the person has been using. i remember one person was a high school student. he came to us because he wanted to stop, but couldn't. we showed him how slow the brain activity, and he stopped! his got so much better within just a month.
medicinally, i say do what you've got to do. i don't want anyone to be in pain, that is too cruel. but needing it to function is like needing.. any addictive food really. idk, my friend in college would say she took excellent notes in class when she smoked first. but her speech was slower, and she said the dumbest things, lol! i could always tell when she was smoking by that.