Gamma-aminobutyric acid (GABAGamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter in your brain, meaning it slows your brain's functions. GABA is known for producing a calming effect.) is an inhibitory neurotransmitter in your brain, meaning it slows your brain’s functions. GABAGamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter in your brain, meaning it slows your brain's functions. GABA is known for producing a calming effect. is known for producing a calming effect.