Green Xanax Bars S903 is a benzodiazepine that increases the activity and functions of GABA (Gamma-aminobutyric acid), a neurotransmitter known as an inhibitor. This inhibitory neurotransmitter in the CNS blocks the transmission of chemical messages into the brain cells. As a result, it lowers brain cell excitation and neural excitability, making you feel calm and relaxed. Green Xanax Bars start to work within 15 to 20 minutes and last 7 to 8 hours in the system. Green Xanax, on the other hand, has a half-life of 11.6 hours.