you said lately which means he wasn't like this in recent past. Pay attention to what he is doing along with how he is acting. Has his friends changed, did he drop out of or join any new groups lately. Does he have any new friends or stopped talking to old ones. I know its hard to get into a teen's mind but look for clues that could tell you things and casually ask questions. Kids hate it but try to know the people he is hanging out with. Be aware of his life, know where he's going, what he's doing and who he's with as much as possible. If he's not hanging out with old friends and not really making new ones, the old ones could have picked up a habit that he didn't like and he's conflicted on how to deal with it. If he's made new friends they could be influencing his behaviors. Look at your behavior and his fathers, have ther been any family changes? As much as we hate to think of it, any and almost every teen is going to experiment with drugs and or alcohol at some point. Pay attention to his eyes and if he's able to look you in the eyes, look for glassy, red, small pupils, squinty - I'm sure you know the signs. No matter what the cause is you need to be a strong parent and let him know that this behavior will not be accepted and there will be consequences.