Reference

GABA (gamma-Aminobutyric acid) is a neurotransmitter used by the central nervous system to reduce neuronal excitability. In the brain GABA is involved in processes related to organization, equilibrium, and rest. Optimal GABA function results in a healthy response to nervous system stimulation as well as recovery from overstimulation.

GABA is necessary for downregulating neuronal excitability. Without GABA, overstimulation by other neurotransmitters would occur, resulting in seizures and eventually death. Throughout the body, GABA is utilized for rest states, such as sleeping and exercise recovery.

While the body tends to balance the amount of GABA vs glutamate needed, GABA can be artificially increased with certain drugs. Most of these drugs function as analogues with a high affinity for absorption/reception and thus often result in rapid tolerance.

GABA depletion can occur from failing to obtain adequate glutamine from the diet. Since most sources of glutamine are animal derived, vegans & vegetarians are most at risk of GABA deficiency. Excessive exercise as well as chronic alcohol consumption can also lower systemic GABA levels.

Consuming foods rich in glutamine, such as meat, eggs, nuts, and seeds.
Supplementing with GABA cofactors, precursors, & augmentors
Regularly engaging in activities that involve organizing, meditating, relaxing, or otherwise reduce overstimulation.