Yeah, What Oldroadie said. My kids were th SH** at that age and we found out later it was pot, and other delectables. We never would have thought it. But it was true. Funny, when we were doing that stuff while living at home we tried to blend in and avoid conflict. They do not seem to do that these days.
They are also just trying to pull away and exercise their independence at that age. That is all fine and good if they can keep up their responsibilities. That could be part of it too.
Best of luck, I remember that was a very agonizing era of my parenting. I does pass, in most cases, and now my kids are great, respectful and productive.
They still think I am a Dork...