General Discussion

There's an scene where he collapses in the passageway to the stage on his way to do a show. Colonel Parker (who you'll hate by the end of the movie) says "The only thing that's important is that man is on stage in 10 minutes."! The doc shoots him full of something, and the next scene is Elvis on stage jumping and gyrating.
My guess is whatever that shit they were using on Elvis was, it's probably a real close relative of what they use on that idiot whenever he's got to, you know, function as a human