Xanax( Alprazolam) is a benzo ( benzodiazepine) used to treat anxiety, seizure, and panic disorders. Yellow XANAX Bars R039 is a rectangular pill in yellow, and the best part is that you can break it two equally to take the dose. In addition, it is potent and robust for managing symptoms effectively. Yellow XANAX Bars R039 is a powerful formulation that will help you manage anxiety as it increases GABA activity and helps relieve bouts of anxiety. The drug's effect begins within one hour, and the duration of action is six to eight hours.