I don't know if it's useful to you or not, but let me give you the example of two kids I know: one of my friends since childhood, Bianca, and my brother George. Bianca was so difficult to deal with in high school (she's 21 now), that her mother cried all over that she lost her daughter. She was into drinking, parties, smoking, all sort of bad entourage. My parents many times told me that I would ruin my reputation if I talked to her, even tried to forbid me to see her, but I didn't care. I said just wait until she grows a little up, when she would have to leave her friends to do to university, and guess what happened? All of that stopped when I'd said it'd stop. She's fine now, she has a job, she goes to university, she's into projects there and it all goes well.
My brother George was close to not passing the bacalaureat, but he did. He's 19 now. He has all those friends my parents hate and does all the teenager stuff like smoking, drinking, is away from home all day and almost all night, but he's been admitted to a good college and, mostly, like Bianca, he'll be in the same situation, he'll go away from his friends and he will have a sort of normal time for a young man.
I don't know, my examples don't seem to be the best, but there's what I wanna say: their bodies heal very fast, for example, they're very young. The same happenes to their mind, it changes very fast, they're in search of an identity. It's ok, you're a parent, you're worried... But be a little patient 'cause once they have something for sure and they know what to do in life, it all gets easier.