J.S.Mill set the groundwork for this in his book On Liberty. Which says that people should be allowed to do whatever they like – as long as they do not harm others. If they want to drink themselves to death – they should be allowed to do that – as long as they do not harm their dependents.
As a practical matter, as many families have found to their sorrow, alcoholism usually cannot be stopped. I have know some alcoholics who have recovered, and they go insane whenever they see a liquor store. It’s hard for them to let other people make their own decisions about drinking.
The same approach could apply to any drug.