It is not indicated for anxiety disorder. For anxiety, alprazolam immediate release is often taken as needed because the onset is quick and duration is short. For frequent panic attacks, alprazolam can be taken around the clock to prevent attacks, which may be triggered by certain situation or condition. When alprazolam immediate release is taken around the clock, it may produce unwanted side effects due to fluctuation in blood concentration. The difference between the Xanax XR and immediate release is that the XR formulation has a slower rate of absorption, longer duration and has a more constant blood level.