In case you aren't, being able to do what you want with your own body does not include a right to harm others. Remember, we are talking about ingesting drugs, not hitting other people.
Is there a point at which drug use should be considered antisocial and unacceptable?
You have to make the argument that drug use doesn’t harm others. In a libertarian thought experiment maybe it doesn’t, but in the real world it does.
In particular, we tend to criminalise behaviors that increase the risk of harming others. Consider drunk driving. Nobody is harmed if I don’t have an accident. But the risk of an accident increases, so we criminalize it. The same is true of hard drugs. The probability I will harm others conditional on meth addiction is higher than the background probability.
And yes, you can prosecute them for whatever property or violent crimes they commit, but for the victim, it’s too late! They have already suffered. A better outcome is if we decrease the amount of usage of drugs like meth and fentanyl via law enforcement, and subsequently decrease the externalities that society has to bear.
