Well, I suppose it would depend on the specific methodology of the study. What I'm wondering about is if the doctor prescribing it had no idea there were such a thing in play. Honestly I can't think of any way it could be done without creating an ethical dilemma but maybe a creative researcher could figure that out. With my admittedly limited understanding of the effect I would guess that it would produce the exact same result as if it were just the patient who thought it was a real drug.