The question of expense raises doubts about how this plays out in a nationalized health care system like the one in Spain, where I live. Here, patients would be unaware of the costs of their medications and procedures, as they're all covered. Given that a significant percentage of the positive results patients experience are due to the placebo effect, one wonders whether it wouldn't be better in some cases to make patients pay something -- even a token fee -- for some treatments where this effect is more likely.
I've been interested in the placebo effect for a long time—but this is a thorny issue, starting with the question of how much a "token" fee is. Dan's study found that that a placebo painkiller that cost $2.50 worked much better than one that cost ten cents. You can read about the experiment in Dan's book, or see Ben Carey's article in the New York Times.
Does this mean that making patients pay a small copay would produce better results than giving them free health care? Not necessarily. Since, as Dan explains, the mechanism behind the placebo effect is a patient's expectations, it might be less a matter of what the patient pays out of her own pocket and more a matter of the perceived value of the procedure. I'd bet if a patient underwent surgery and were told the procedure cost $12,000 but that the government would pay for it, she would fare better than a patient who was told the procedure cost $200 but that her copay was $50.
Charging a patient a "token fee" could even have the effect of anchoring that small number in their head and reducing the effectiveness of a medical treatment. Maybe charging no copay at all would be preferable.