Yellow Xanax bars are a form of the drug alprazolam, which belongs to a class of drugs called benzodiazepines. These drugs enhance the activity of a neurotransmitter called gamma-aminobutyric acid (GABA) in the brain. GABA is an inhibitory neurotransmitter that helps to regulate activity in the brain and nervous system. Enhancing the activity of GABA produces a calming and sedative effect, reducing feelings of anxiety and promoting relaxation. This can be helpful for people who suffer from anxiety disorders, panic disorders, and other conditions that cause anxiety and stress.