I've come across a few things referencing placebos lately, in particular 'transparent' or 'open' placebos where the fact that it contains no known effective ingredient is not hidden.
One is a link to this research on "Effects of open-label placebos in clinical trials: a systematic review and meta-analysis" from Nature dated Feb 16, 2021:
Open-label placebos (OLPs) are placebos without deception in the sense that patients know that they are receiving a placebo. The objective of our study is to systematically review and analyze the effect of OLPs in comparison to no treatment in clinical trials.
We found a significant overall effect (standardized mean difference = 0.72, 95% Cl 0.39–1.05, p < 0.0001, I2 = 76%) of OLP. Thus, OLPs appear to be a promising treatment in different conditions but the respective research is in its infancy.
Then in perusing Andy Clark's latest book The Experience Machine, which posits the brain as a prediction engine, constantly engaging with sensory input both consciously and unconsciously to enable action, he concludes with some material about what he refers to as 'honest' placebos:
Honest placebos appear to work by activating subterranean expectations through superficial indicators of reliability and efficacy such as good packaging and professional presentation (foil and blister packs, familiar font, size and uniformity of the pills, and so on). This is because - as we have seen - the bulk of the brain's prediction empire is nonconscious.
Clark reviews a number of other findings in his 'Hacking the Prediction Machine' chapter, and in a sense concludes:
In the end, it looks like anything that can be done to increase our confidence in an intervention, procedure, or outcome is likely to have real benefits.
He also describes use of certain psychedelic drugs as having the potential to 'reset' the prediction machine in very useful ways.
