I’m all for humiliation as a behavior modification tool.
Buy one of these boxes, put a luggage alarm http://www.amazon.com/s/?ie=UTF8&keywords=luggage+alarm in with a few pill bottles, and leave it clearly marked BECK’S MEDICINE in the medicine cabinet. The next time Aunt NosyWTFIsWrongWithYou goes thru your stuff, pulls the box out and starts shaking it and sets of the alarm… You won’t have to say a word. Other relatives will mumble not-very-quietly “Oh my gosh, did you hear that Sadie tried to steal codeine/viagra/xanax from Beck? …So sad, I hope she gets the help she needs…” over the next couple of years