Is Taking Gaba Supplements For Anxiety Just Hype?

GABA is a byproduct of the KREBS cycle which synthesizes the fuel that powers brain cells, so any normally functioning brain has an abundance of it. Indeed, there is so much that the Blood-Brain-Barrier is adapted to pump GABA out of the brain's extracellular fluid into the blood stream for elimination. See:

http://www.jstage.jst.go.jp/article/yakushi/124/11/124_791/_article
http://www3.interscience.wiley.com/journal/120707128/abstract

Furthermore, the brain is so efficient at up-taking GABA that it is effectively a built-in mechanism for ensuring that GABA has only very local effects around the synapses from which it is released - i.e. extraneous GABA is sucked up before it can get anywhere near a GABAergic synapse. Neuron slices bathed in GABA rich fluid in test tubes to avoid the BBB issue just don't react to it, only to that released from local synapses.

As an aside, GABA analogues such as the seizure medication gabapentine, which can cross the BBB, do not interact with the GABAergic neurons but affect the glutamate system.

People with anxiety (or epilepsy) are not deficient in GABA, but they do have fewer/impaired GABA binding sites (receptors). Trying to alleviate either of these disorders by increasing the amount of GABA in the brain is akin to topping up the gas/petrol tank to fix faulty spark plugs. It just won't work. If it did our brains would be hostage to our stomachs!

Ian