Despite (or perhaps because of) my stout libertarian principles on the subject of drugs, that any consenting adult should be allowed to ingest whatever substances they choose, I'm all in favour of things like drug rehab.
The thing is you see, that they are addictive. Some are pharmocologically so (or physically) and others psychologically, but there's no doubt that addiction can and does occur. At this point the drug taker is no longer really consenting.
The problem then becomes where to find the drug rehab required? How to find a place that deals with that specific problem, in the way that is needed? Click through either of those links to get to a service that does exactly this. Offers a non-profit guide to where and how you can access the treatment that you or a loved one needs.
Just because I think that drug legalisation is the correct answer doesn't mean I can't acknowledge that drugs do indeed cause problems, and that some will always need help to overcome those.