Well obviously you can't preach at him, but lend a helping hand and listen to him, but you need to get him into that state of self-awareness. If the acid isn't doing it for him then I would suggest ayahuasca or mescaline.
If he's big into trips at the moment then he'll be up for it and he will probably have some important revelations on it. Obviously you need to be there to talk to him and discuss any revelations he has. I can't stress how important it is that it comes from him originally though, even if in your response you direct his thoughts a particular way. E.G stressing the importance of living in the present and letting go of the past.
Also the anti-depressant qualities of aya could work wonders on him.
I had a similar friend who was on a self-destructive path, and I posted on here about it actually, a few years ago. He was big into forest parties and squat raves as well, and was basically nocturnal, working nights in a hospital. He refused to do aya and just took loads of speed and K, and in the end there was little I could do except be there for him. Now, finally, after about 4 years he's sorted his head out (without psychedelics), he's paid me and others back money he owes and seems to be genuinely happy at last.
I guess what I'm saying is, offer him help to begin with, but if he resists it then maybe it's best to let him discover it for himself. I believe that good people come good in the end.
"Language is a cracked kettle on which we beat out tunes for bears to dance to, while all the time we long to move the stars to pity." - Flaubert
I do not engage in or condone illegal activities. Most of what I write is on behalf of people I've bumped into, usually several years ago and in countries where the things I mention are legal.