I know a guy who, 15 years ago, had a bad opiate addiction and somehow maintained his job as a railroad engineer. I don’t know how he got away with it.
The story had a happy ending. He somehow got over it and is now working up the management ranks at the railroad.
I don't know your friend, but it's likely that he's not really "over it." The truest thing anyone ever said is that that, "All drug addicts lie. Every last one." Most of them become quite expert at it, too.