Stimulants such as cocaine and amphetamines are popular recreational drugs, which are thought to be used by up to 52 million individuals worldwide (UNODC, 2010). However, despite their high addictive liability, not everyone who uses these drugs develops dependence, though the risk for dependence is significantly increased for people with a family history of addiction. This familial aggregation of drug and alcohol dependence suggests that either genetic factors, a shared family environment, or an interaction of genes and environment underlie the increased risk for addiction in some people. The concept of endophentoypes may offer a useful tool to better understand how a pre-existing vulnerability to addiction might be inherited. Endophenotypes have been described as neurobiological correlates of a disorder, which are thought to be genetically determined and stable over time (Gottesman and Gould, 2003). In other words, abnormalities in brain systems underlying the clinical symptoms of stimulant dependence may not only be observed in individuals who are dependent on stimulant drugs, but also in their non-dependent first-degree relatives. Key symptoms of stimulant dependence, such as the inability to stop using the drug and the loss of control over drug intake, may be underpinned by a general lack of self-control, which may have predated drug-taking.

These findings shed new light on addiction vulnerability and may explain why the risk of becoming addicted to drugs is increased in people with a family history. The observation that abnormalities in brain and behavior may render individuals vulnerable to developing dependence (if resilience factors are absent), opens up new avenues for preventative and therapeutic strategies. For example, preventative approaches may consider strengthening self-control abilities in individuals at risk, while therapeutic interventions could be guided by the successful compensatory strategies used by unaffected siblings to overcome their brain abnormalities in every-day life. The identification of addiction endophenotypes in brain and behavior provide further compelling evidence that drug dependence is a disorder of the brain, with underlying abnormalities that can increase a person’s risk for addiction.

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