when you can't think of a dentist without thinking of a possible vicodin script even though you'd have to take the whole bottle of vicodin at once just to keep you out of withdrawal. then you might be a junky.
when it takes you an hour of staring at the the television to realize that you've been watching an infomercial on cleaning products for an hour, and you couldn't be happier about it. then you might be a junky, or at least really high.
when at least once or twice a year you have to sit down and have a talk with various friends or family members and reassure them that you are not on heroin and you're not a coke addict, all the while rationalizing in your head that it's true because you're not using heroin or coke, just morphine and adderall. possibly a junky.
when every morning before you go to sleep you erase the history of your web browsing activities on your laptop because you don't want your loved ones to know the extent of your drug obsessions just in case you never wake up from OD'ing on all the pills you took to get to sleep.