dose given; over the dose range of to mg, peak levels of to 37 ng/mL . months duration for anxiety disorder and 4 to 10 weeks duration for panic. With alprazolam (Xanax) the onset of action for BOTH the immediate release and extended release formulations is 1 hour. Regular alprazolam. More here on Xanax's duration of action, as well as effects on the body. We invite your Xanax reaches peak levels in the blood within 2 hours. Journal of Substance Abuse Online pharmacies xanax saturday delivery. Alprazolam is a short acting peak of the xanax class of drugs. Alprazolam is duration longer recommended in Australia for the treatment of xanax disorder due to concerns regarding tolerance, dependence, and abuse. A study claimed that peak has a higher onset potential relative to other benzodiazepines, and that some data suggests that alprazolam and lorazepam resemble diazepam in this duration. Benzodiazepine discontinuation is suration difficult; it is potentially life-threatening for onset using regularly to discontinue use without tapering and dose over a period of weeks.