Gamma-amino butyric acid is one of the major inhibitory neurotransmitters in humans. Genes encoding the GABA(A) receptor subunits, a family of ligand-gated ionotropic receptors, reside in clusters across several chromosomes, including chromosome 4, 5, 15 and X. GABA(C) is another family of ionotropic receptors but their impact on addictions in humans is largely unstudied [85-87].Genes encoding subunits of the metabotropic GABA(B) receptors are being actively investigated in human studies of smoking cessation. Baclofen [88], a GABAB agonist, has also been found to have therapeutic potential in alcohol and cocaine dependence [89-91] .
