Exact mechanism not definitively known; however, in vitro experiments demonstrate that it enhances activity of gamma-aminobutyric acid (GABA). It is thought that binding to GABA uptake carrier inhibits uptake of GABA into presynaptic neurons, allowing availability of increased amount of GABA to postsynaptic neurons. Based on in vitro studies, tiagabine does not inhibit uptake of dopamine, norepinephrine, serotonin, glutamate, or choline.