Source Naturals, GABA Powder, 8 oz (226.8 g)Dietary Supplement Gamma Aminobutyric Acid Supports a Calm Mood GABA (gamma aminobutyric acid) is an amino acid derivative and a key inhibitory neurotransmitter. Neurotransmitters are chemical messengers that carry information between nerve cells or from nerve cells to other target cells. GABA is synthesized directly from glutamic acid. It has an inhibitory effect on the firing of neurons and supports a calm mood.