Psych meds are very different from anything else. They're designed to get into the brain and and add something that the brain may be lacking. Like Insulin. You always need to keep taking it 'cause your body doesn't make enough but you never become used to it and stop needing it.
It's the same principle, only it's more complex. 'Cause brain chemistry is very complex and is not yet completely understood.
So don't worry about that, be glad you have something that helps. If you have something that's worked for 7 years, i don't think you're going to have any problems.