The placebo effect is real apparently even
The placebo effect is real apparently even when you know it's a placebo, and, alternately, the possibility exists that cultural expectations of whether a drug works may have an effect on how well the drug works:
There are various possible interpretations of this finding: it's possible, of course, that it was a function of changing research protocols. But one possibility is that the older drug became less effective after new ones were brought in, because of deteriorating medical belief in it.