The biology of addiction.

The tools of modern genetics and neurobiology have propelled a renaissance of research that has advanced our understanding of the pathophysiology of drug addiction. We know that an individual's risk for addiction is determined by interactions between genetics and environment and that only a minute fraction of chemical agents share the ability to act on this vulnerability to induce a state of addiction. Repeated exposure to these drugs causes addiction through repeated activation of dopaminergic transmission (and many other actions) in the brain, inducing changes at the molecular, cellular, and synaptic levels that, over time, rewire the circuitry throughout the limbic system. In this Review, I discuss how we are gaining a clearer picture of this drug-induced plasticity-some of which is shared by all addictive drugs, whereas other aspects are specific to certain drug classes-and of the ways in which these adaptations mediate the range of behavioral abnormalities that define the addicted state. Despite the challenges, there is reason for optimism in translating this rich biological understanding of addiction into improved treatments for the many individuals burdened by this illness around the world.