GABA (gamma-aminobutyric acid) is an amino acid that functions as a neurotransmitter in the brain. GABA is synthesized in the brain from another amino acid, glutamate, and functions as an inhibitory neurotransmitter – meaning that it blocks nerve impulses. In the body, GABA is concentrated in the hypothalamus region of the brain and is known to play a role in the overall functioning of the pituitary gland – which regulates growth hormone synthesis, sleep cycles, and body temperature.