Your friend is right that both Adderall and Red Bull are stimulants, and so is nicotine. In people with ADD / ADHD, stimulants actually act to calm them mentally, but I think the effect on the heart is still the same as with a non ADD person.
If your doctor is aware of your Red Bull intake, then you should be fine. You could mention it again just to be on the safe side, next time you see him / her.
I *would* suggest that you space it out a little...like, don't wash down your pill with a Red Bull while smoking a cigarette
