That is not the definition of a placebo.
You take the placebo (whatever it is: could be a pill; could be some kind of task or routine) and you believe it is medicine; you believe it to be therapeutic.
The placebo effect comes from your faith, your belief, and your anticipation that it will heal.
If the pharmacist hands you a pill and says, “here, this placebo is sugar!” they have destroyed the effect from the start.
Once on e.r. I heard the physicians preparing to administer “Obecalp”, which is a perfectly cromulent “drug brand”, but also unlikely to alert a nearby patient about their true intent.