Here's the last thing. I don't treat my family except for basic, everyday stuff. They don't listed to me...proximity bias.
If your dad wants to feel better, I suggest you try to find a doctor that agrees with your viewpoints. Tell your dad that the only way he will get "a pill for it" is to go see the doctor. Then let the doctor take care of it...he will likely listen to someone, anyone else more than you...that's just the way it is.