I know an RX does have a lot of powers to change some things, like the brand without talking to a dr. or at least the ones here in Canada do. The RXs have a lot of schooling on all these medications, treatments ect. If you have a history with an RX, they know which brands are better for you.

Ex. I can get a prescription for Birth Control Pill & I can leave with Birth Control Patch.

I had a horrible reaction to the ulser meds I was on when I was 16yrs old.. the Dr. gave me the same stuff I told my RX what this did to me last time, so she gave me a different brand with diff stuff in it, to see if it reacted with me better. It didn't so she gave me Zantec75 instead.. that helped a lot (I lost so much weight cause my body didn't want to eat due to the pain food caused)...

But always questioning the Dr. about it is a good idea, you never know.