a type of drug that works by enhancing the action of the neurotransmitter gaba
gamma-Aminobutyric acid In general, GABA does not cross the blood–brain barrier,[50] although certain areas of the brain that have no effective blood–brain barrier, such as the periventricular nucleus, can be reached by drugs such as systemically injected GABA.[57] At least one study suggests that orally administered GABA increases the amount of human growth hormone (HGH).[58] GABA directly injected to the brain has been reported to have both stimulatory and inhibitory effects on the production of growth hormone, depending on the physiology of the individual.[57] Certain pro-drugs of GABA (ex. picamilon) have been developed to permeate the blood–brain barrier, then separate into GABA and the carrier molecule once inside the brain. This allows for a direct increase of GABA levels throughout all areas of the brain, in a manner following the distribution pattern of the pro-drug prior to metabolism.[citation needed]