[Neurobiological basis of drug addiction]

INTRODUCTION. Drugs of abuse cause addiction, characterized by compulsive and out of control drug use. Several neurochemical and molecular changes take place in the brain during the first phase of drug use which lead to dependence, addiction and drug abuse. DEVELOPMENT. Every drug of abuse acts through similar neurophysiological mechanisms, mostly based on the abnormal activation of the mesolimbic dopamine system. Although the addicted brain tries to adapted to the drug action, there are permanent neural changes at the cellular and molecular levels which seem to underlie the addictive process and the emergence of abstinence symptoms after drug taking stops. Furthermore, these neural changes appear to subserve the emergence of cravings once the abstinent syndrome has been overcome. Cravings are the main factor leading to relapse, and they are often initiated by exposure to drug related cues.