Why do you think teenagers start doing drugs? Or drinking? Or other self-harming behaviors? I agree (with you), some do engage in it just for experimentation, or for thrill seeking. However, there are those who do it to ease troubles, numb pains, and to cover up struggles.
I want to offer some understanding of why adolescents do drugs and alcohol. Explanations not excuses, because there are other ways, healthier ways, of handling anger.
Self-harming behaviors, like drinking, using drugs, or blatantly misbehaving in school can be indicators of troubles at home, or in another personal venue. I feel it is best to consider a well-documented example.
In 1994, The Fifth Estate and later Frontline, aired a documentary called The Trouble With Evan. It was about a mother and a father that were trying to figure out why their child was stealing and acting out violently in school. Mom and dad were attending support classes and everything to try and "solve" their problem child. Their good parenting efforts were fruitless and the parents turned to outside help.
The Fifth Estate came in, set up cameras in the house and revealed the secrets. There was abuse, no physical evidence found on Evan, because it was psychological abuse. The parents were hurting the family pet, calling him names, and threatening his safety. Evan was acting out as a way to ask for help, he was only eleven and didn't know how to say: "My dad is kicking the cat in front of me. I am being told that I will be locked up in a cage." He was indirectly asking for help, by acting out. To the public, it looked like Evan had a terrible temperament that could not be controlled, but in the home, this was the source of the misbehavior.
Even over 15 years later, it is the same, when teenagers and children misbehave, it can be an expression for help in a way that they cannot explain, nor sometimes want to say. Which is, for example, often the case for sexual abuse victims.
Feel what it would be like, being betrayed by someone you love, harming your safety, holding and sometimes taking your treasured valuables away from you. The one place, home, where you ought to feel safe is danger. You can pretend to be ill to not go to school, but you must always return home after school. Where are you to turn, when no one will turn to you? Who is there to help you, when those who are supposed to help are violating your trust? How else can you ease the pain?
Now, I don't want to plant seeds excuses. This is not meant to sound as an excuse; it is an explanation of why.
We need to be ready to assist those who are displaying signs of extra assistance. Don't just pass them off as ill tempered.
If you are developing a dependency to cancel out the mists of darkness, seek out help in whatever way you can. Despite having some well traveled avenues of trust burned, there are still many less traveled roads of trust that can get you the help that you are looking for.