Identifying the changes that occur in the brain as a result of alcohol and other drug (AOD) use is important to understanding the development of AOD addiction. The nerve cell signaling chemical (i.e., neurotransmitter) γ-aminobutync acid (GABA) plays an important role in the brain chemistry of addiction. Most drugs interact with binding molecules (i.e., receptors) for specific neurotransmitters and either block or facilitate binding at these receptors. Thus, cannabis and opiates act via receptors intended for internally derived (i.e., endogenous) cannabinoid and opiate substances. In contrast, alcohol does not appear to activate specific receptors. However, alcohol influences the activity of many transmitter systems including GABA and endogenous opioids and cannabinoids.