Hi , As per ur description, cannabis is just a small part of the problem. A much greater resolution is required at a psychological level. It will be much better if a change in his environment will be a productive thing to do at this point. A full time caring at a rehabilitative centre will be of greater help. Only care to be taken is dat the place b equipped with regular counselling and consultation from psychiatrists. It may seem too big a step at this point but it will be too late beyond this point. I guess this helps but feel free to consult further. Take care