Although in chemical terms it is an amino acid, GABA is rarely referred to as such in the scientific or medical communities, because the term "amino acid," used without a qualifier, by convention refers to the alpha amino acids, which GABA is not, nor is it considered to be incorporated into proteins.

In spastic diplegia in humans, GABA absorption becomes impaired by nerves damaged from the condition's upper motor neuron lesion, which leads to hypertonia of the muscles signaled by those nerves that can no longer absorb GABA.

A number of commercial sources sell formulations of GABA for use as a dietary supplement, sometimes for sublingual administration. These sources typically claim that the supplement has a calming effect. These claims are not utterly unreasonable given the nature of GABA in human sympatholysis, but GABA as a tranquilizing agent, purely isolated in itself, is scientifically unsubstantiated or only irregularly demonstrated.^{[citation needed]} For example, there is evidence stating that the calming effects of GABA can be observed in the human brain after administration of GABA as an oral supplement.^[49] However, there is also more scientifically and medicinally relevant evidence that pure GABA does not cross the blood–brain barrier at therapeutically significant levels.^[40] While GABA may not cross the BBB, it is important to note that studies have shown that, within stressed individuals, GABA does indeed have a positive effect, albeit with side effects.^[50]The only way to deliver GABA effectively is to circumvent the blood-brain barrier. Indeed, there are a small, limited number of over-the-counter supplements that are derivatives of GABA, such as phenibut and picamilon. Picamilon combines niacin and GABA and crosses the blood–brain barrier as a prodrug that later hydrolyzes into GABA and niacin.^[51]