I have really bad panic attacks whenever I have to travel via planes. My doctor prescribed xanax 0.5m and said to take 1 30 min before my flight and then 1 every 4 hrs. I of course had friends and family saying that I should take half of 1, others say half of a half, so I thought I'd try half of one the other night just to see how out of it I would be. Nothing happened, so I took the other half 4 hrs later and still nothing. The next day I took 1 whole pill and still nothing. Does xanax only work if you're actually having a panic attack? My sister said I drink lots of coffee and soda and caffeine probably reduces the effects of the drug. Im really feeling anxious about this since my flight is for next Friday the 12th of Nov 2010. Any ideas?