A GABA transaminase inhibitor is a drug that acts as an inhibitor of the enzyme GABA transaminase (GABA-T), which metabolizes the major inhibitory neurotransmitter ó-aminobutyric acid (GABA). Inhibition of GABA-T reduces the degradation of GABA, leading to increased neuronal GABA concentrations. Examples of GABA-T inhibitors include valproic acid, vigabatrin, phenylethylidenehydrazine (PEH) (a metabolite of phenelzine), ethanolamine-O-sulfate (EOS), and L-cycloserine, among others. Certain GABA-T inhibitors, like vigabatrin, are used clinically as anticonvulsants.