Teenagers with bad friends
As a parent you hope that your teenager will be popular at school and that they grow up with childhood friends they keep through to adulthood. Many television programs depict friendship as tolerant and enriching and available to all, but always beneficial. The problems arise when the friends your teenager hangs around with are none of those things. Choosing their friends is the first independent thing your child does as they grow up. When they are little their friends are the children of your friends, parents who meet in the labor ward of the maternity hospital and then become friends, relatives, close neighbors.
Once they go to high school they are exposed to children from a much wider area and they get to choose who to be friends with themselves, without your input. They will visit these new friends and go to different neighborhoods and meet other people and make more friendship choices.
Sometimes teenagers make bad choices and the friends they hang around with are trouble. They can decide to be with these people precisely because they know their parents would not approve, it is a form of rebellion. It may be that these negative friends show the teenager a world they have never seen, a carefree attitude to life without responsibility that seems very attractive. These bad friends are exciting; they break rules, and often the law, and seem totally unbothered by it. This can seem like courage in teenagers' eyes rather than irresponsibility.
You may not approve of some of your teenagers friends, but you are unlikely to meet the really bad ones, teens are smart enough to keep those friends away from you. Instead they will go over to the new friends' house, to study, to hang out, away from your scrutiny and able to behave in a totally different way. If drugs are part of the culture of this friendship group then your teenager will try drugs, as part of fitting in, but also as an act of defiance, they know you would not approve. The arrogance of youth is that they think they know more about current drugs and how to take them "safely" than their stuffy parents, who may actually know a good deal more than their teenagers realize!
If they are taking drugs and drinking alcohol with these new friends, you will notice a change in their behavior, an increase in talking back at you, staying out later each time, refusing to discuss their friends with you. Physically the drugs will affect them and emotionally they will become less stable. Separate the friendship from the addiction; you can try to ban them seeing these friends, with more or less success, but the important area to deal with is the addiction, whether to alcohol or drugs. If their behavior is really bad, you should choose a residential recovery program; they need to be totally removed from all the influences that aid the addiction. Part of the program will be about educating them to make good choices in the future, including understanding what true friendship looks like.