Gamma-Aminobutyric Acid is a naturally occurring neurotransmitter with central nervous system (CNS) inhibitory activity. Gamma-aminobutyric acid (GABA), converted from the principal excitatory neurotransmitter glutamate in the brain, plays a role in regulating neuronal excitability by binding to its receptors, GABA-A and GABA-B, and thereby causing ion channel opening, hyperpolarization and eventually inhibition of neurotransmission. 
GABA acts to slow down signals between neurons, making neurons less electrically excitable. 
Studies also show that It plays a role in neuronal stem cell differentiation, possibly giving it an important role in adult brain plasticity. 
Recently, research showed that with an increase in nitric oxide, GABA could more easily cross the blood brain barrier. Nitric oxide also causes GABA release in the hippocampus . In a recent study, GABA supplementation by itself increased brain GABA 33%, but when combined with L-arginine, a stimulator of nitric oxide, brain GABA rose 383.3%. 
We chose to use L-Citrulline as the NO-booster in GABA Brain Food because it has been shown to be a more effective NO booster than L-Arginine [6,7,8,9]
Rosmarinic acid, present in rosemary, lemon balm, and other herbal agents known for their calming properties, inhibits GABA-transaminase, which slows the breakdown of GABA 
Grape Seed Extract
Grape Seed Extract can also upregulate the eNOS enzyme for a further boost to nitric oxide 
The National Center for Complementary and Integrative Health (NCCIH) is currently supporting research and studies on other potential abilities of grape seed extract to support healthy cellular function. 
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- Salazar P, Velasco-velázquez MA, Velasco I. GABA effects during neuronal differentiation of stem cells. Neurochem Res. 2008;33(8):1546-57. PMID 18357524
- Getting SJ, Segieth J, Ahmad S, Biggs CS, Whitton PS. Biphasic modulation of GABA release by nitric oxide in the hippocampus of freely moving rats in vivo. Brain Res. 1996;717(1-2):196-9. PMID 8738273
- Boonstra E, De kleijn R, Colzato LS, Alkemade A, Forstmann BU, Nieuwenhuis S. Neurotransmitters as food supplements: the effects of GABA on brain and behavior. Front Psychol. 2015;6:1520. PMID 26500584
- Examine: L-Citrulline. Examine.com
- Kuhn, K. P., et al. Oral citrulline effectively elevates plasma arginine levels for 24 hours in normal volunteers. Circulation 2002; 106: II1–766S.
- Schwedhelm, E., et al. "Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism," British Journal of Clinical Pharmacology, 65(1):51-9, 2008.
- Stephen J. Bailey, et. al. L-Citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans. J Appl Physiol 119: 385–395, 2015.
- Awad R, Muhammad A, Durst T, Trudeau VL, Arnason JT. Bioassay-guided fractionation of lemon balm (Melissa officinalis L.) using an in vitro measure of GABA transaminase activity. Phytother Res. 2009;23(8):1075-81.PMID 19165747
- Feng Z, Wei RB, Hong Q, Cui SY, Chen XM. Grape seed extract enhances eNOS expression and NO production through regulating calcium-mediated AKT phosphorylation in H2O2-treated endothelium. Cell Biol Int. 2010;34(10):1055-61. PMID 20513234
- US Department of Health and Human Services. National Institute of Health Database. Grape Seed Extract. The National Center for Complementary and Integrative Health (NCCIH)