Only if the medication doesn’t work. The evidence is that placebos don’t work. Mostly, the placebo effect is a statistical illusion.

It is plausible that the body will expend more energy to combat a disease if you are (sub-)consciously convinced that you are cared for and don’t need to stress. Stress hormones down-regulate the immune response. Cortisol, used for treatment of autoimmune disorders like asthma and allergies, is a stress hormone.

But a sham treatment could also have the opposite effect. If your subconscious understands that as a signal that you must get back into action, you may end up releasing stress hormones. These psychological effects are just too idiosyncratic and fickle to be used reliably.

Stuff like broken bones or cancer doesn’t respond to psychology at all. The body is already doing all it can.