Actually, studies have shown that placebos work sometimes even when people know. This is a great podcast about this topic and the page also has links to some studies: https://www.npr.org/2019/04/29/718227789/all-the-worlds-a-st...
I wonder what the results would have been with a less suggestive presentation.
[1] https://journals.plos.org/plosone/article?id=10.1371/journal...
> “That’s absurd!” sputters Mark. “I don’t believe in magic that works whether or not you believe in it!”
> “I said that too,” chimes in Autrey. “Apparently I was wrong.”
https://www.lesswrong.com/posts/X3HpE8tMXz4m4w6Rz/the-simple...