GABA

This entry defines GABA as the brain's own signaling chemical, a mechanism term. It does not assess GABA sold as a supplement; that evidence is on the GABA compound page.

Cortical excitability reflects a balance between excitation and inhibition, and GABA supplies the inhibitory side [1]. The brain makes GABA from glutamate [1], using an enzyme called glutamic acid decarboxylase that comes in two separate forms [1].

GABA works on two timescales. Released at synapses, it produces fast "phasic" inhibition [2]. A small amount outside cells, called GABA tone, produces a slower "tonic" current that also controls neuronal activity [2]. Some of that tone comes from support cells such as astrocytes, which release GABA by routes other than synaptic vesicles [2].

GABA taken by mouth raises a question this definition cannot answer: whether it reaches the brain at all. A 2015 review noted that GABA had long been thought unable to cross the blood-brain barrier, but that the studies on the question were often contradictory and used widely different methods [3]. The same review called for studies that measure brain GABA after oral doses, for example with magnetic resonance spectroscopy [3].

So the brain's GABA system and a GABA supplement are different subjects. When an article says a product "increases GABA," read it as a mechanism claim. Our compound pages grade outcomes measured in people, such as sleep or stress ratings, separately from mechanism.

• Glutamate
• Neurotransmitter
• Blood-brain barrier