I found myself getting addicted to Oxy's when I got out of the hospital and Vicodin's aka Oxycodene. You know the feeling that you get when an orgasm happens? Or a rush of excitement? That is what it feels like when you are on an oxycontin. You have this rush in you but all you want to do is chill out and enjoy the feeling of no pain and you can't even begin to feel upset by anything.
To say it numbs you would be an understatement.
Vicodin is hydrocodone...slightly different and a bit weaker.
I would guess Rush took what he could get.