z4My best friend's girlfriend went through a similar situation with severe depression and she was trying to kill herself. My friend said that you just have to be there for them, make them happy, do everything with them. In this case where drugs are involved, if it's possible you need to contact parents, police, etc. he's probably going to hate you for doing things like that but you're saving his life. In the end he will understand, hopefully you can do everything in your power to save your friend.
As someone who struggles with depression, this is true, but there's also only so much a friend can do. As much as it sucks, sometimes you have to let them fight through it themselves and hope for the best.
I will say though, It's a weird feeling when you're contemplating ending your life if you know someone cares about you. There are days you start thinking no one cares, no one would miss me, it's a scary place. Gotta make sure they realize just how much they matter, and no matter how bad life gets, it gets better. You have no idea how big a difference those last two make.