“The term placebo effect is generally used to include a variety of things, including expectation effects, and usually it also helps control for things like regression to the mean which, obviously, is not an “effect” of the placebo. In its strictest sense there is no such thing as a placebo “effect” because by definition, placebos are substances without an effect. But that usage strikes me as pedantic. The term placebo effect, when used to encompass all of the aspects of the difference between a drug group and a control group, is helpful and, I think, operationalized well enough to be clear.” Obviously not. If ‘placebo effect’ exclusively meant “the aspects of the difference between a drug group and a control group” it would be impossible to do placebo controlled trials of non-drug therapies. That clearly isn’t the case. The trial you are reviewing was not of the traditional ayahuasca healing ceremonies of the people of the Amazon. To introduce them by claiming they rely on the placebo effect is just as gratuitous as if a pill doctor reviewing a placebo controlled neuroleptic trial claimed that therapeutic communities such as Soteria rely on the placebo effect because the patients (by and large) don’t take neuroleptics. To know whether the ceremonies you mentioned rely on the placebo effect you’d have to run a trial in which one arm used the actual ceremony and another arm used a sham ceremony which resembled it but lacked the aspects practitioners claimed were what brought about healing (e.g. by having the shaman take a sugar pill). The trial you review does no such thing, so to suggest it says anything about whether traditional ceremonies rely on the placebo effect is false. To suggest you know anything about whether such ceremonies rely on the placebo effect is also false because no such trials have been done (at least to my knowledge – please correct me if I’m wrong). “Yes, the researchers in this paper CALLED it a limitation. However, while the researchers called this a lower dose, there’s really nothing to compare it to. It’s not as if there is an established dose of ayahuasca for clinical work. So, the researchers note that their dose was just somewhat lower than in two other studies.” So if they gave a microdose – or even a zero dose – it wouldn’t have been a limitation because there’s no established benchmark to compare it to? Perhaps. If so it’s equally true to say there’s no dosage that would be relevant to the study because we don’t know which ones might be therapeutic. So it’s a non-study that shows nothing. But there is something to compare it to. The placebo controlled trials which had neither the limitation of subjects with no clinical symptoms to alleviate nor a lower dose than has been found to have therapeutic effects. And they found “significant antidepressant effects of ayahuasca when compared with placebo at all-time points”. https://pubmed.ncbi.nlm.nih.gov/29903051/ Obviously if you lower the dose sufficiently from there you will eventually reach a point at which it doesn’t have significant effects, so if this trial hadn’t had the additional limitation of lacking depression symptoms to treat it would be reasonable to say it shows a sub-clinical dose of ayahuasca, not that it shows the placebo effect in action (or at least not any more than any placebo controlled trial of anything does).