4-(trimethylammonio)butanoate is an amino-acid betaine gamma-aminobutyric acid zwitterion in which all of the hydrogens attached to the nitrogen are replaced by methyl groups. It has a role as a human metabolite and an Escherichia coli metabolite. It derives from a gamma-aminobutyrate and a gamma-aminobutyric acid zwitterion. It is a conjugate base of a 4-(trimethylammonio)butanoic acid.