Used as a stable isotope-labeled internal standard in mass spectrometry and HPLC analyses for the accurate quantification of GABA (gamma-aminobutyric acid) in biological samples such as plasma, cerebrospinal fluid, and brain tissue. Its deuterated structure allows clear differentiation from endogenous GABA, improving measurement precision in neurochemical and metabolic studies. Also employed in tracer experiments to monitor GABA metabolism and neurotransmitter dynamics without altering biological activity.