Incredibly, the placebo effect is (mostly) not real. It is a result of statistical confusion. Whenever you have a group with extreme values, they tend to exhibit regression to the mean. Eg. on average, sick people tend to become more healthy over time. Thus if you give one group medicine, and one group placebo, the placebo group will also tend to get better over time, because of regression to the mean. People have then misinterpreted this to think that it is the placebo pill that actively does this. If you want to demonstrate a placebo effect, you have to construct a study where there are three groups: • A. treatment • B. placebo • C. no treatment, no placebo If B and C get different outcomes, that would demonstrate a placebo effect. When this has been tried, mainly there has been no provable placebo effect. See the paper in the screenshot. (There is some evidence for an effect for pain, but this get's into a slightly different debate.) The fact that the placebo effect is mainly not real, fortunately frees us from having to come up with convoluted explanations, as to why the placebo effect would work even when we tell the patient that it is a placebo, as in the quoted tweet.