As with GABA, glycine is an inhibitory neurotransmitter. Its action is mediated through the glycine receptor, which is localized to certain areas of the CNS including the spinal cord and brain stem. This means that activation of this receptor with a small molecule is less likely to cause psychiatric side effects than a GABAA receptor modulator. In addition, glycine receptor modulators are expected to be more effective for certain indications such as pain.
Figure: The glycine receptor.