Now, as people know, I'm from hte libertarian end of the political spectrum (classically liberal if you wish) and I'm adamant in everyone's freedom to ingest absolutely whatever it is that they wish, yes, even at the risk (or even certainty) of harm to themselves.
However, this is (as it has to be) balanced by an acknowledgment that there also has to be an effective system of Drug Treatment for those who have become addicted. That can be to alcohol or to drugs, even to certain forms of behaviour themselves, and while it can be difficult it is indeed possible.
Indeed, centres like The Watershed exist to do exactly that, to help people who do not want to be taking drugs to get off them.
This might sound a little odd, insisting that people should be allowed to take drugs and also insisting that treatment should be available to those who do not want to. But that's exactly the point, it's a matter of human freedom. Those who wish to do something should be at liberty to do so. Those who are involuntarily drawn to it by illness, should be aided in their cure.
Odd perhaps, but then that's being a liberal for you.