I think some people believe prescribing a medicine is more important than making sure the patient doesn't die from it though.
Very true.
I also think some people believe that substituting the states "superior" judgement over that of an individual, even if one disagrees with that individuals judgement call, is something to be desired.
I don't see how even the most tortured reading of the commerce clause can support that so I'm guessing the right to always get some medication is covered in the penumbra of the Constitution. Or maybe it's rooted in Scottish law.