If the demons control your body by abusing your brain and nerve impulses, it could be. Our bodies work through electrical signals and various neurotransmitters like serotonin, so an anti-psychotic that affects brain receptors could prevent such a "hotwiring".

Would it be any different than if aliens could beam signals to individual neurons to force you to do something? What about a skilled surgeon with an Arduino, or those seizure prevention circuits they can install?

The antipsychotics turn the body bitter, making it less comfortable for the demon. Hence the demon leaves for a better target.

Well, probably not. But if demon possessions were a real thing there is no reason why only medieval remedies should be effective against them