It's really scary when you think that your child might be using or abusing drugs. I think you really have to watch if their behavior changes because it will immediately. Look at the friends they're hanging out with. Do you like them? Do you trust them? Do you know them? If they walk in your house and they can't look at you to say hello. Follow them to their bedroom, open the door and look them in the eye. Smell t hem. Give them a hug. I've hugged my kids just to see if I can smell anything on them. If you really suspect that there is something going on, look on their backpack. Look on their computer. I'm also valuing my children's privacy but if i think there's a reason that I need to look a little deeper into something then I will and I think that's absolutely our right and I think it's our responsibility to do some investigative work and really keep searching until you're satisfied. If you find there's a problem then that's another question.