Alprazolam side effects?

My 12 yr old cat was prescribed alprazolam 0.25 mg for our drive to Florida from Boston. We stop 2 nights so it's not so much time in the car as it sounds but my cat ( this is her 3rd yr driving down) gets really anxious and goes right for my dads lap and down to his feet while he's driving and nearly causes an accident.
I don't like keeping her in her carrier which would be safe I know but seems cruel and she sometimes wants to lie down with me in back but it takes hours before she stops yelling and jumping all around the car like crazy.
I want HER to be relaxed and safe, it is not so my cat won't make noise and i dont want her zonked out cause I love her voice and company. I just want a safe ride without having to grab her from dads lap before getting near the gas pedal and break~ that's the first place she heads for.
My vet prescribed alprazolam to be given 30-60 minutes before the drive and suggested giving her a dose at home first to see how it affects her.
Does anyone know the side effects of this and if there's anything I should watch for or expect?
Nervous mama here when it comes to giving an 8lb cat a sedative for the first time.
Any help would be appreciated!
;-)

Kiera, you should probably put this in a new topic. I see this is your first post, so you probably did that by mistake--look for the "Start a New Thread" button on the top-left of the screen when you're in the "Cat Health" forum.

Alprazolam is an anti-anxiety medication; it is also used for humans under the brand name Xanax. It's the sort of sedative you'd be given before minor surgery where you stay awake for it, to stop you from freaking out; or for short term treatment of anxiety disorders or panic attacks, or given to you to take before a plane ride if you are afraid of flying, that kind of thing. Your cat will probably be less likely to panic, and she may be sleepy as well. Your vet's advice about trying a dose at home makes sense; occasionally a cat will have what's called a "paradoxical reaction", which actually makes the cat hyperactive; and some cats get an upset stomach from taking the pill; so if yours is one of those then obviously it won't work for her. But this is unlikely. Most cats tolerate it just fine.