Vistaril (hydroxyzine pamoate) acts quickly. It is rapidly absorbed into your stomach, and begins to work as soon as 15 to 30 minutes after you take it. To treat motion sickness, for example, your doctor may prescribe a pill or tablet, and tell you to take it 30 minutes before you travel. It is also prescribed to treat hives and other allergy symptoms as well as anxiety. While it acts quickly, it is not known how effective it is over a long period of time. Vistaril has not been studied in clinical trials for the treatment of anxiety for longer than four weeks. If you find your Vistaril prescription is not working as well as it has been, make an appointment to see your doctor and talk about it.