How do I help my friend who is struggling with addiction?

Today my friend K was not her self this morning, she is usually shy and keeps to herself unless she is around her friends so it was unusual seeing her acting crazy for tweeting out a little, she always wears makeup yet didnt today and his hair was going crazy. Me and my friend E were worried back her and I was gonna talk to talk to her about what was going on and in my 2nd period with her and she starting BALLING HEF EYES OUT. And she the teacher made me go to the bathroom with her and she was tweeking out and crying yet laughing and I thought she was gonna hurt me if im being honest. She told me she was hung over from her mom giving her drinks last night and she didn’t feel well but I know that wasn’t it, my teacher and I including her went to the office which sent us to this special consolers office and I dropped her off. I came back soon after to drop off lunch that I bought her and she was still crying uncontrollably. After lunch I came back again to give K her phone when me and the consoler had a conversation. K had just got put on antidepressants and when I told the teacher that she got scared because drinking and antidepressants dont go well together and make you act how K did, so I got more worried and I waited in the office with K till her mom came. (Ps in the bathroom she was telling me how she just wanted to be sober, not from only drinking but smoking but she doesn’t know how, because her mom makes her smoke because it’s am antidepressants and she grows it too). In addition my friend N  who is friends with her boyfriend L, told me that L told N that he actually got her drinks last night and now im scared. L is older than K and is failing all his classes so Thats way he is in freshman classes and now he met K. L is just not a good influence to K and I don’t want her to going down in addiction even more. 

If anyone as any ideas of what I can do please tell me, btw this all happened today