GABA is the major inhibitory neurotransmitter in the central nervous system. It fulfills a number of functions in the brain and affects nonneuronal tissues outside the brain. GABA regulates many depressive and sedative actions and is critical for relaxation.^{[7][8][9][10]} Consequently, several drugs that resemble the structure of GABA (e.g., baclofen, gabapentin, and pregabalin) have been developed to treat seizures and convulsions. GABA is also involved in the neural regulation of visual tasks and emotion processing.^[11]

In general, there is limited human research on oral supplementation with GABA. A few small studies have found improvements in sleep quality and markers of stress, as measured by questionnaires, heart rate variability, and cortisol, following supplementation with GABA, but other studies have not.^[1] Therefore, it’s not currently possible to draw firm conclusions about the effect of GABA on these outcomes.

Some studies find that supplementation with GABA improves some aspects of visual attention^[3] and mood during stressful tasks.^[2] These effects might be relevant to people with schizophrenia and mood disorders because GABA levels in the brain and neural signaling processes activated by GABA are altered in these conditions.^{[12][13][1][14][15][16]} However, studies determining the effect of supplementation with GABA in people with these conditions is currently lacking.

A single dose of GABA (1 gram) taken orally has been shown to blunt the rise in core temperature at rest and during exercise in the heat,^[17][18] but it remains to be studied whether this effect can actually help improve exercise performance in the heat.

One resistance training intervention found that daily supplementation with whey protein (10 grams per day) and GABA (100 milligrams per day) increased fat-free mass more than whey protein alone,^[19] but muscle strength was not affected. Further studies are needed to confirm this finding.

Ingested GABA does not appear to reach the brain in appreciable amounts,^{[20][21][22][23]} meaning oral supplementation can’t be assumed to replicate the effects of GABA as a neurotransmitter. However, the main drawback is that few studies have examined the effect of oral supplementation with GABA in humans. Furthermore, the specific effect of GABA is often difficult to determine because many human studies examine the effect of eating GABA-containing foods, like tea or rice, rather than the effect of oral supplementation with GABA alone.^[1] Consequently, further clinical trials specifically using GABA are needed to fully understand its effects.

Oral supplementation with GABA appears to be fairly safe and well-tolerated, with no evidence of toxicity in animal studies^[24][25] or serious side effects in human studies.^{[26][25][27][17][18][19][1]} However, abdominal discomfort, headache, and drowsiness has been documented following supplementation with GABA.^[28]

GABA exerts its various effects by binding to GABA_A and GABA_B receptors in the brain. GABA is also found outside the brain in nonneuronal tissues, including the pancreas, certain immune cells (e.g., lymphocytes), and the gastrointestinal tract. How GABA works outside the brain is an area of ongoing research.^{[7][8][9][10][10]}