What is the effect of a supplement with GABA for depression?
GABA = Gamma-Aminobutryic Acid is a neurotransmitter of the brain, which inhibits some relevant transmission of impulses within the cns-network. GABA is an amino-acid which is manufactured in the brain. But it cannot pass the blood-brain barrier. So any additional supplement to the food or pills will have no effect, because the drug won´t come to the place of action.
Many online-pharmacies try to promote the use of GABA to relief anxiety, depression or promote stimulation of growth hormones.
Any effect of this approach would be a placebo effect! There is no scientific evaluation of the use of GABA for these indication.