This is a great question, even if you don't have an adolescent in addiction treatment. Because there are times during those precarious "in between child and adult" years when every parent asks, "how do I know for certain whether he/she is telling the truth?"
And the obvious answer to that question is: you don't.
(I can just hear you thinking, " Great insight Kim, that was so worth the 3 seconds it took me to read"...)
Listen, I fully admit to being an expert at nothing. However, I do have a plethora of experience in kid-related matters. If I haven't encountered it personally in my own life, or through the lives of my children, I have read about it.
All of that being said, I wish I could tell you there is a simple formula which will ensure continual trustworthy behavior from your child. Instead, what I offer you as a mother of five, someone who works in the counseling field, and a former adolescent myself is this: clichés.
Yes, clichés. Two of them in fact.
1. Trust takes time to build, and you cannot rush time.
When kids mess up and get caught they may fess up completely and feel like that's enough to earn back trust. But the truth of the matter is you should never blindly trust once you have seen it isn't in your favor to do so. Nor is it in the best interest of your child. So, as much as your kiddo wants you to move on and get back to trusting him/her again, that just isn't realistic...and, in fact, it is foolish on your part. As with any relationship, trust doesn't happen overnight which leads me to cliché number two...
2. What is it they say? A man (or woman) with nothing to hide, hides nothing. Don't be afraid to ask yourself the hard questions such as are your child's words and actions in sync? Are they upfront with cell phone/computer conversations? Does your child make eye contact with you when you converse? Do you know with whom and what they are doing when they are out? Do you know what they are doing when they are under your roof for that matter...How well, if at all, do you know the parents of your kid's friends?
I have found [by trial and error in my own parenting] it is crucial to put the bulk of my trust in my own instincts. I love my children, but they entered the world not as perfect human beings rather as those capable of wrong-doing and, at times, capable of falling into temptation. So in order for me to do the best job I can as their guide and protector, I need to look no further than their behavior to gauge how much trust to give.
Akin to these two basic, yet never too often conveyed clichés... what you DON'T hear is often more important than what you do.
Trust is earned in increments, with each example of "walking the talk and talking the walk" the ability to gain it back grows.