Gamma-aminobutyric acid (GABA) is both an amino acid and a major inhibitory neurotransmitter in the central nervous system (CNS), where it plays a major role in cellular communication. GABA may provide nutritive support for a positive mood, healthy relaxation and the moderation of anxiety through its regulation of neuronal excitability. Recent research suggests that in addition to its inhibitory action in the CNS, GABA has a parallel inhibitory role in the immune system and may modulate inflammation.