What Should I Do?
Ask Questions
Ask other adults in your child's life if they have noticed changes in behavior. A good place to start is at their 
school - talk with their teachers, counselors, or coach. Most schools now have prevention specialists on the counseling staff who can help.
Communicate
Communicating with your child is very important. If they are reluctant to talk, enlist the aid of his guidance counselor, doctor, or a local drug treatment referral and assessment center.
Explore what could be going on in your child's emotional or social life that might prompt drug use. Is there anything going on at home or school that could be responsible for his shift in behavior?
Even when the signs are obvious, parents sometimes have difficulty admitting that their child could have a problem. If your child is using drugs, it is important to avoid blaming yourself for the problem and to get help as soon as possible.
Be Consistent
Be consistent in enforcing whatever punishment your family has chosen for this type of rule violation. Do not give in just because your child promises never to do it again.
Get Help
Depending upon the severity of your child's drug use, you will probably need help to intervene. There are many local programs available that specialize in helping families just like yours.