Glutamate is intimately linked to addictive behaviors.
See the following link about how brain neurotransmitters like Glutamate and
GABA are affected by alcohol and other drugs linked to substance abuse:
http://gslc.genetics.utah.edu/units/addiction/reward/pathways.cfm
GABA is created from MSG and may be addictive. GABA fits the same receptors in the
brain as valium. Glutamate also stimulates the NMDA (N-Methyl D-Aspartate) receptors
in the brain. These receptors are currently being investigated for their role in
Long Term Depression. Taurine, which is adversely affected by glutamate has shown
some promise in treating drug addiction.