hmmm.... knock them out then check them into rehab. or just call the cops on them. i've seen quite a few people get clean after either happened to them. but if it's rehab, it's gotta be the 24 hour, away from home kind.
Show them a picture of their future 10 years from now, pale, pasty, sores, scratching all the time, paranoid, no teeth, and thats the lucky ones.... the others are dead or in jail.