Here is a list of problems that could indicate drug use. Be careful not to automatically assume, however, that drugs are the problem. Children, especially adolescents, give off many of these signals when they are distressed in other ways, too. You'll need to sort out with your child exactly what the problem is and try to identify any substance abuse, perhaps with the help of a family counselor or child psychologist. Keep in mind that even if there is no drug abuse going on yet, these other problems need to be addressed.
1. Increased truancy and tardiness to classes
2. A drop in grades
3. Behavior problems in school
4. Losing interest in activities the child once enjoyed
5. Dropping old friends and a sudden influence of a new crowd
6. Personality changes -- a child who was once outgoing is now withdrawn, or someone who is usually relaxed is now fidgety much of the time
7. Sudden mood changes -- euphoria followed by tenseness or edginess; excessive suspiciousness or paranoia