They should be able to.

That would be a good way to reduce the efficiency of the remaining antibiotics very quickly.

(But also, this kind of thing is exactly why the analogy doesn't even make sense.)

You're right. This is a good reason to restrict this class of drugs. There is a finite usefulness, oh which each person who uses them consumes a tiny little bit.

They should not, because the adverse consequences are not limited to the individual.

You can't be serious, right? I don't even want to imagine how many people would accidentally kill themselves or at least seriously damage their health if that was the status quo.

Is that my job to prevent? If someone wants to do the most damaging things possible, to intentionally kill themselves, should I feel entitled to stop it?

People should be free to do stupid things, so long as they don't hurt others (the antibiotics example that another poster gave us a much stronger argument)

This sounds like a libertarian take, in the sense of "libertarians are like housecats - convinced of their own fierce independence but totally dependent on systems they neither control nor understand".

I'd be interested to hear your original thoughts on why my position is incorrect.

There are prescription drugs with side effects that cause real second-order societal problems (OxyCodone and related opioids are one the come to mind immediately). Amphetamines can cause psychotic behavior (see https://en.wikipedia.org/wiki/Stimulant_psychosis for an accessible read). If the person using and abusing those drugs were isolated from others and couldn't harm them it would be one thing but they usually aren't.