Let's think about this for a bit.
Xanax *yes, that's how it's spelled!* is a legal drug.
Yes, it is only available by prescription, but any type of security could tell from looking at it that it was a pharmaceutical pill and not a tab of 'xtc' or something.
If the doctor gave you some antibiotics, and you had to travel with them, would you worry about taking them on the plane?
What if the pills in your antibiotic bottle weren't antibiotics? Do you think some dumb airport security guard would be able to tell the difference? NO. All he sees is a prescription bottle with your name on it...
I'm being too nice, as you can see, but really this isn't even a question you should even have to ask.
Of course, I am presuming that these xanax are your meds and that you have a prescription for them and that all of this is kosher...