Selective, non-transportable inhibitor of GlyT1 which displays no activity on GlyT2 or the transport of proline, GABA or glutamate (IC50 values are 2.8, 9.8 and 56000 nM for hGlyT1, rGlyT1 and rGlyT2 respectively). Enhances the amplitude of the NMDA component of glutamatergic EPSCs.