There are a number of signs and signals that are held up as universal indictators that your kids are doing drugs. Falling grades, radical shifts in groups or friends, constant need for money, really big personality changes. All of these things are supposed to indicate that your child is doing drugs. The problem is that it also indicates a child that is in puberty.
It is really not helpful to have a list of things for which you then assign your kid's drug use because they are exhibiting those behaviors. One of the things about determining whether a kid has drug and alcohol use as part of their lives is, basically, seeing patterns and variations off those patterns over time. One of the best things a parent can do to recognize patterns in their children's lives is to meet them at the door when they come home from socializing with their friends.
When your kid comes home, you need to spend five minutes at the kitchen table with them discussing how their night went. If your kid is out on the town and they picture coming home and talking to you for five minutes, they can't do that completely slaughtered. They can't do it drunk and they can't do it high. Greeting them at the door insures that they have to come home sober or you are going to catch them.
One of the best things about this is, as your kids get older, if your bedtime precedes your kid's curfew, there is a lot of things that can go wrong. Here's what we do. Don't go to bed in your kid's bed. Don't fall asleep at the kitchen table in a puddle of your own drool. That really lowers your authority position. Here's what you do. You go to sleep in your kid's bed. When they come home, they have to get you up and out of it before they can get into it. It is perfect. It is unbeatable and, by far, the most positively recommended review we have at parent meetings. Sleep in your kids' beds.
One of the other things parents are tempted to do to check and see if their kids are doing drugs and alcohol is to drug test their kids. That's got a lot of pitfalls involved in it. Two situations where we would recommend that drug testing is appropriate. One is where the parent and child agree that drug testing will be a part of the child's resistant skill set. In other words, "I can't, you guys, my parents drug test me." Or in the case of a completely lost, uncooperative, confrontational teenager, where you are trying to figure out what's going on, and you want to find out if it's drugs and alcohol. Those two circumstance, we would go along with drug testing.