Tiagabine-d6 is intended for use as an internal standard for the quantification of tiagabine by GC- or LC-MS. Tiagabine is an inhibitor of GABA transporter 1. It inhibits seizures induced by DMCM in mice. Tiagabine reduces allodynia in a rodent model of neuropathic pain when used at a dose of 72.8 µmol/kg, and it acts synergistically with gabapentin to delay pain responses in mice in the hot plate test. Formulations containing tiagabine have been used as adjunctive therapies in the treatment of partial seizures.