Here's the drug classification info per Wikipedia.org for Celexa & Xanax. You can find more information on their website or elsewhere:
Citalopram, (trade names: Celexa, Cipramil) is an antidepressant drug of the selective serotonin reuptake inhibitor (SSRI) class. It has U.S. Food and Drug Administration (FDA) approval to treat major depression, and is prescribed off-label for a number of anxiety conditions.
Alprazolam (trade name Xanax, available among other generic names) is a short-acting anxiolytic of the benzodiazepine class of psychoactive drugs. Alprazolam, like other benzodiazepines, binds to specific sites on the GABA gamma-amino-butyric acid receptor. Alprazolam is commonly used and FDA approved for the treatment of panic disorder, and anxiety disorders, such as generalized anxiety disorder (GAD) or social anxiety disorder (SAD).