What is the outcome when taking Vistaril with Xanax?

The interaction is moderate, meaning:

Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.

Interactions between your drugs
Moderate
ALPRAZolam hydrOXYzine
Applies to: Xanax (alprazolam), Vistaril (hydroxyzine)

Using ALPRAZolam together with hydrOXYzine may increase side effects such as dizziness, drowsiness, confusion, and difficulty concentrating. Some people, especially the elderly, may also experience impairment in thinking, judgment, and motor coordination. You should avoid or limit the use of alcohol while being treated with these medications. Also avoid activities requiring mental alertness such as driving or operating hazardous machinery until you know how the medications affect you. Talk to your doctor if you have any questions or concerns. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

Source and more info: https://www.drugs.com/interactions-check.php?drug_list=1303-775,133-54