The idea of modern medicine is to sell chemical compounds that actually have an effect. It’s a philosophical and ethical thing. All products have a unique psychological effect that gets intertwined with their biochemical effect. If you can’t study them individually, it’s impossible to tell if the biochemical effect even exists at all. If your medicine relies heavily, or even entirely, on the psychological side, it’s no different than homeopathy. The idea of modern medicine is to be better than the old stuff that preceded it.
I prefer to think of this as an equation like this: Pm+Bm=Pp+Bp
Pm=psychological effect, medicine
Bm=biochemical effect, medicine
Pp=psychological effect, placebo = surprisingly big
Bp=biochemical effect, placebo = 0
If these sides are equivalent, the medicine is just as effective as placebo. If the medicine side is bigger, you’ll want to know how much of it comes from the P and B terms. In order to figure that out, you would need to know some values. Normally, you can just assume that Pm=Pp, but if you can’t assume that, it you’re left with two unknowns in that equation. In this case, you really can’t assume them to be equal, which means that your data won’t allow you to figure out how much of the total effect comes from psychological and biochemical effects. It could be 50/50, 10/90, who knows. That sort of uncertainty is a serious problem, because of the philosophical and ethical side of developing medicine.