One thing that has been mentioned in multiple other threads is that Rush would not be able to do his show so well if he was strung out on oxycontin.
That is especially true if you are starting out with a hearing deficit. Although the cochlear implant is a vast improvement for him, he still has a hearing deficit as compared to someone his age with normal hearing.
Anytime you have a physicial deficit, it becomes embellished with illness or intoxication. However, he has been as sharp as a tack ever since he had that implant.