Ingested GABA does not appear to reach the brain in appreciable amounts,[1][2][3][4] 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.[5] 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[6][7] or serious side effects in human studies.[8][7][9][10][11][12][5] However, abdominal discomfort, headache, and drowsiness has been documented following supplementation with GABA.[13]