" And I understand a placebo isn't necessarily a negative. "
I'm not sure you understand, rather I think you've misunderstood. In the absence of positive (demonstrated) evidence that something has been shown to have some particular effect, the default is in the negative - there is no effect. Not that taking it is a negative.
Using a placebo is a nothing - no effect, no consequence.
Placebos are used for and in double blind testing (research), not for treating patients. I doubt if any doctor would ever prescribe or provide a placebo to a patient to treat an ailment, illness, or medical condition.
Q