Presumably a lot depends on whether the person is looking for state-run rehab covered by their medical insurance, or seeks and can afford a high level of comfort.
Australia, New Zealand and South Africa each have a luxury rehab industry, sometimes in remote settings, with a lot of extras such as sports, massage, etc., to help the person get through withdrawal, and probably more psychotherapy to try to deal with the underlying issues.
One of the disadvantages, so I was told, of such treatment in Switzerland (whether state or private) is the geography and the infrastructure. More or less, there is a bus-stop within walking distance of the gate of the treatment facility, which potentially takes one to access to drugs or alcohol. One has to bring a determination to try to avoid that.
I think ongoing support afterwards is essential. It is illusory to imagine that one can check in for the 6 weeks or 3 months, get clean, do some introspection, talk to those who're on the same road, and then step back out into Real Life and be just fine. I mention this because a friend who did a rehab said he had had exactly that notion when he entered the clinic, and indeed, had only agreed to go because he had thought along those lines.
He said he was shocked to learn that some of his co-patients were in for a second or third time. As he spoke to them, he realised that the single, destroying factor was that they had gotten clean, gone home, and let everything get back to normal.... and crashed because they did not know how to navigate "normal" differently , when their home and especially their social environment had gone on just the same while they were away.
He said one of the hardest things to accept was that, after he had gotten clean and gone home, he would need to actively seek out and participate in a support group, perhaps several groups, one each evening if need be, on an ongoing basis, perhaps even for life , to help keep him on the right road.
He did so, though, because he really, really knew that persisting in his addiction would mean certain death. He also knew that family members had paid for the rehab, and that they would not be able to do so for a second round.
He found a 12-step programme. He told me that while some people there are nice, he doesn't even like most of the people who attend, but seeing them once a week (or more) to share experiences and on account of that coping clean for the whole time, is soooo much better than crashing. He also finds comfort in being able to encourage others to stay clean.
6 years now, all good!
Here's quite a good outline of what is actually done in a rehab clinic.
https://www.addictioncenter.com/reha...cal-day-rehab/