gamma-Aminobutyric acid, usually referred to by the abbreviation GABA is a neurotransmitter that inhibits the transmission of nerve impulses. In humans, it also regulates muscle tone. Although it is chemically related to the amino acids, it is not used in the synthesis of proteins.

Several anti-anxiety drugs work by effectively increasing the level of GABA, either by acting in the same manner or increasing its production.

gamma-Aminobutyric acid at Wikipedia