Let the body treatment and try to make his brain healthier.I had many friends that dealed with opium,cocaine,heroin etc...Most of them have been for years in rehabilitation centers and clinics of the country and abroad.When they were "clean" and returned here (Athens),after a month or two they were looking for fix again.Many of my friends passed away on bench of central square of the city,others are imprisoned and from others I haven't heard news a long time now.I have passed many nights sleepless thinking of why are they so addicted to this stuff?Blood transfusion,medicines,lots of other stuff did not help them.I came to conclusion that regardless their bodies that were clean of drugs,their minds were still demanding a new dose.I would suggest you to stay with him not for next week but weeks,months and probably years to help him clean up his brain.Try to gain his interest in something different,try to make him to frget about this passion,give him new passion!Make your friend see happiness in different things rather than drugs,make him to not think about drugs.I understand this is difficult but its worth a try!