Gamma-aminobutyric acid (GABA) is the chief inhibitory neurotransmitter in the mammalian central nervous system. It is a non-proteinogenic amino acid synthesized from glutamate via glutamic acid decarboxylase (GAD). GABA binds to GABA-A and GABA-B receptors to hyperpolarize neurons, reducing excitability and promoting relaxation, sleep, and anxiety reduction. In foods, it occurs naturally in fermented products like kimchi and tea. As a supplement, it is studied for stress relief and blood pressure modulation. Chemically stable under physiological conditions, it is highly polar due to its amino and carboxylic groups. It does not cross the blood-brain barrier efficiently when ingested orally.