Boy, one of these again... These suck...

Ok, heres the basics..

1] He won't stop because you want him to(you found this out already).
2] You can't make him stop(short of putting him in a hospital or mourge).
3] It's not always 'once a tweaker, always a tweaker'. My kids mom was one when we met, she has been clean since around the time we got married, and still is today..

Those are the simple facts... Now for what you can try to do..

First off, you can gently break it to him that he's an addict.
You can ask him why he's trying to kill himself.(he may not realise it yet)
You can offer to help him find a program, With no promises about the future.
You can call the cops when you know he's holding. They will arrest him and it might help him see the possibilities of non-usage.(if he finds out it was you, give up, he won't listen to you ever)
You can tell him that you can't even be a friend if he's gonna do this, That your not willing to watch him kill himself.(see the one above)
You could, through a third-trusable- party, inform his parents.(unless they use too, or don't care, then it's useless)

YOu can continue with these things till you decide to give up, or till it works..
*hands you a coin* flip this for answer...

As much as you don't want to hear it.... You can't "make" him stop, he has to want to do it himself.. Until he decides that he wants to give it up, all you can do is gently nudge his brain to the point HE, yes HE, decides to give it up..
As a last thing to point out to you.. remember this
-----DO NOT make any promises to him EVER that you aren't willing to carry though with------



End Of Rant.....
Hope this helps in some way..