Before taking action, it is wise to learn as much as you can about drug or alcohol abuse in teens.  Good sources are www.TheAntiDrug.com or www.freevibe.com on the web.  You also may wish to call the National Clearinghouse for Drug and Alcohol Information (NCDAI).  They will send you pamphlets about dealing with substance abuse problems and can be reached at 1-800-788-2800.  You can dial "211" to talk with an informed person who knows about the resources in your community. 

Talking with your teen about substance abuse is a difficult task for most parents.  It's an emotional and frightening subject.  Parents often feel that if their teen has a substance problem that it is their fault.  Parents may feel that their authority is compromised because they are presently or have in the past struggled with a substance-use problem.  Even though this may be the case, parents are still in a better position to understand the causes and consequences of substance misuse than is a teen.  Parents have a right and obligation to intervene if their child is using drugs or alcohol.  You don't have to be perfect to be right.

Prior to sitting down with your teen, make a plan for talking about the main issues and don't lose sight of these issues throughout the discussion. Try to choose a time when the tensions in the house are at a low ebb and when you and your teen have enough time to talk. Then, when you do sit down with your teen, tell them about your concern for their wellbeing.  Be genuine and avoid scare tactics.  

When you feel that you have laid out the reason for your concern, get your child's point of view.  You don't have to agree with them, but listen carefully and try to see the world from their perspective.  Try to form a partnership with them for solving the problem.  If you are successful, you have taken an important first step toward resolution.  Set firm but reasonable rules for your teen that clearly define your expectations and that allow your teen to regain trust and appropriate independence.

If the attempt at forming an alliance fails the first time, try again on another occasion.  If, after repeated attempts, you feel that you are not  able to succeed with this effort, it is time to seek  professional help.  The following is a list of resources that you might engage in this effort:

Remember that, although parents don't have absolute control over the choices that teens make, parents are never-the-less important resources for providing structure, love and good information for children.

http://theantidrug.com/ei/conversations_teen.asp