Why is your grandfather taking this medicine? Uh, because you told me to.

I went with my grandfather to the doctor today. As his doctor was going over his medicines, he looked at a bottle, looked at me, and then asked me,"Who prescribed this medicine?" My response, "Uh, you did."  He then told me, "No, I didn't, he doesn't need it."  Normally , I would have had a smart mouth retort but I decided to hold my tongue. But it made me think, why would I go out and buy my grandfather a medicine without consulting his doctor?  I'm not a health care professional but I am pretty thorough about what he takes- I double check his prescriptions, try to be careful when filling his pill box, and stay on top of his medical conditions. I wouldn't just decide to pull something out of my @$$ concerning his medicines. Besides, he's been taking this particular prescription for almost two years, we always take all his pill bottles to the doctor, and he just now noticed he's taking something he shouldn't be? Of course, doctors don't make mistakes do they?