GABA is gamma-aminobutyric acid, an inhibitory neurotransmitter formed from glutamine. It is discussed under Glutamic Acid.

Glutathione (GTH) is actually a tripeptide composed of three amino acids—cysteine, glutamic acid, and glycine. Cysteine is the important amino acid here; it controls the amount of glutathione made in the liver and gives GTH its metabolic power as an antioxidant and detoxifier. Since GTH is not easily available or usable by its oral administration (it breaks down into the individual amino acids), L-cysteine is usually supplemented to enhance glutathione production by the liver. Since methionine can be converted to cysteine, it may also be helpful.