Xanax bars are rectangular alprazolam pills which weigh usually 2 milligrams. Brand-name Xanax bars are white. Generic alprazolam bars are typically yellow, green, or blue. Unlike other Xanax bars, blue Xanax bars weigh 1 milligram. How long does a blue Xanax bar last? One dose of blue Xanax can last anywhere from 31 hours to 134.5 hours (5.6 days) in the body, depending on factors related to...