Potent and selective glycine transporter 1 (GlyT1) inhibitor (IC50 values are 15.8 and > 30 000 nM at GlyT1 and GlyT2 respectively). Induces a dose-dependent elevation in CSF levels of glycine, and enhances acetylcholine and dopamine release in the striatum and prefrontal cortex respectively. Produces profound locomotor and respiratory impairments at higher doses.