As other people have said, its an oxymoron surely, i mean yes you can take whatever drugs it is you take and have everything sorted, life is great everything is as it should be, good job, beautiful wife, kids who behave and are gonna go places and you are indulging in your chosen narcotic.
THEN BAM, "yes mr x will you step into my office you have been chosen for a random drug test". Goodbye job and drug funds, people now know about you, will the wife stand by you or will she bugger off with martin from next door, he is stable and only ever has the odd sherry from time to time. Shit man i need a job to live and now (if you are American) your lifestyle has made you ill but you cant pay medical bills and so on and so on.
Obviously that is very far fetched, especially for me, beautiful wife pah, a fuckin troll would be nearer.
When i was clubbing all the time from late 97 to about 2002 i would get spannered every friday through till late sunday takin E and base (pure speed) so i would only start functioning by weds morning so for me no not a success unless to be succesful is dribbling in a corner doing goldfish impressions and going bat shit on the dance floor.
Then i got a job in a hotel the drugs were gone and suddenly i was respectable, i worked hard getting a promotion along the way, then got ill, suddenly now I AM a succesful drug user thanks to cancer as it spread from my balls to my gut into my spine, thankfully it is now in remission but i have so much pain these days. For four years i was on an obscene amount of morphine now it's methadone as it is being used as a painkiller now.
Surely you mean recreationally though.
Maybe there are succesful users, but i don't think there are any sucessful drug abusers.