GABA (gamma-aminobutyric acid) is produced by neurons in the brain, and functions as the principle inhibitory neurotransmitter. GABA is associated with the parasympathetic side of the autonomic nervous system, which balances the sympathetic (fight-or-flight) response. Lower concentrations of GABA have been observed in major depression and post-traumatic stress disorder in the brain, and a region of the brain known as the insular cortex that is associated with emotional response.* Lower insula levels of GABA are associated with significantly higher trait and state anxiety.* GABA, as an inhibitory neurotransmitter, is one of the mediators responsible for reducing the response to fear or anxiety-provoking stimuli.* L-theanine is an amino acid found at high amounts in green tea. L-theanine supports relaxation and mood by increasing alpha-wave activity, and levels of serotonin, dopamine, and GABA in the brain.* L-theanine also has been shown to block binding of L-glutamic acid to excitatory glutamate receptors in the brain.* Glutamate receptor subtypes have been shown to modulate excitability associated with anxiety, while in depression, a hyperfunctioning glutaminergic system also may be an issue.* Continuous administration of L-theanine has been shown to increase expression of brain-derived neurotrophic factor (BDNF) protein, a protein which plays a role in neural plasticity and neurogenesis.