Xanax XR 3mg is a brand name for alprazolam, which belongs to a class of drugs known as benzodiazepines. Benzodiazepines are central nervous system (CNS) depressants that work by enhancing the effects of a neurotransmitter called gamma-aminobutyric acid (GABA). GABA is a neurotransmitter that helps regulate brain activity, and by increasing its effects, Xanax produces a calming and relaxing effect on the brain.