Does that work when you are doubtful that you'll be helped?
Yes, it does - this is (one of the reasons) why medical trials are conducted double blind.
The efficacy of Morphine has been shown to have both physiological and placebo components: It outperforms a plain placebo so we know there is an actual effect, but if you go through the ritual of giving the medicine the efficacy is increased. Also, if you give morphine via a drip then quietly switch the drip for saline, the effect of the morphine continues beyond the point at which it has left the body.
tl:dr; Placebo is weird and awesome, even with real drugs.
The efficacy of Morphine has been shown to have both physiological and placebo components: It outperforms a plain placebo so we know there is an actual effect, but if you go through the ritual of giving the medicine the efficacy is increased. Also, if you give morphine via a drip then quietly switch the drip for saline, the effect of the morphine continues beyond the point at which it has left the body.
tl:dr; Placebo is weird and awesome, even with real drugs.