Probably the oldest question in the book. kids,teens are tricky. and it really does depend a lot on the person everyone's different. Confront them CALMLY and simply talk about it(DO NOT MENTION ANYTHING ABOUT YOU WANTING THEM TO STOP even though that is what your thinking) just talk about it you know why? when? who? what? what ever you want to know. BUt Tred carefully and make sure you think each thing over hundreds of times in your head before you say it. and slowly after talking about it again mention your worried about there health, you wnat them not to do it again.e.t.c and the rest is up to the kid I'm afraid. There response varies WIDELY. It's highly likely they wont say a complete ok i wont do it anymore or NO! LEave me alone i hate you. If it get's really bad you can confront them about going to talk to someone and if they refuse and things get very serious call someone or force them to go. Over time if Things get TERRIBLE even moving on to stronger drugs, drinking you know it's time to start thinking,Rehab. It is very likely they wont want to go. But they have no say. Even if they HATE you. you have to be strong for the both of you and remember it's for there own good. When there older and leading clean happy lives they will thankyou.