But that's the truth, isn't it? From a scientific perspective, it might be interesting to see how well the placebo effect holds up if patients literally think

But that's the truth, isn't it? From a scientific perspective, it might be interesting to see how well the placebo effect holds up if patients literally think it won't work, e.g. by selecting participants who haven't heard of the placebo effect, and not informing them. But from the perspective of helping people, if the placebo effect is to some extent caused by knowledge of the placebo effect, so much the better; there's no deception in that.