It is now clinically understood that the neurotransmitter Dopamine plays a central role in addiction. Most drugs of abuse, with the exception of benzodiazepines, have a direct effect on increasing the dopamine reward cycle in the brain.
Once addicted the mere anticipation of getting high will trigger a marked dopamine response in the addict or alcoholic.
Likewise early recovery from addictions is often hampered by the lack of dopamine d2 receptors that take many months to return to baseline functioning. The lack of sufficient d2 receptors is a primary reason that many drug addicts and alcoholics fail at abstinence during the first 90 days of their recovery.
Rick Murphy, M.A.