My best friend is overusing drugs and alcohol?

I've been best friends with this girl (Sadie) for a long time, and she recently started to hang out more and more with her new best friend April. Me and Sadie aren't as close as we used to be because of girl drama and whatnot, but we are friendly to eachother and hung-out together just the other day. I found out a couple of days ago that whenever Sadie and April hang out, they get high and drunk, and they cause trouble with other people. Sadie already said that April does ecstasy and other drugs, but I didn't think that Sadie would ever go down that road. Just a few weeks ago we were talking about how we felt about people getting high.. I'm really worried about Sadie, but like I said.. We aren't AS close anymore. Should I talk to Sadie about it, or should I let her figure it out on her own? Please help..