Aims. Addiction has been conceptualized as a shift from controlled experimentation to uncontrolled, compulsive patterns of use. Current neurobiological models of addiction emphasize changes within the brain's reward system, such that drugs of abuse 'hijack' this system and bias behaviour towards further drug use. While this model explains the involuntary nature of craving and the motivational drive to continue drug use, it does not explain fully why some addicted individuals are unable to control their drug use when faced with potentially disastrous consequences. In this review, we argue that such maladaptive and uncontrolled behaviour is underpinned by a failure of the brain's inhibitory control mechanisms. Design. Relevant neuroimaging, neuropsychological and clinical studies are reviewed, along with data from our own research. Findings. The current literature suggests that in addition to the brain's reward system, two frontal cortical regions (anterior cingulate and orbitofrontal cortices), critical in inhibitory control over reward-related behaviour, are dysfunctional in addicted individuals. These same regions have been implicated in other compulsive conditions characterized by deficits in inhibitory control over maladaptive behaviours, such as obsessive-compulsive disorder. Conclusions. We propose that in chronically addicted individuals, maladaptive behaviours and high relapse rates may be better conceptualized as being 'compulsive' in nature as a result of dysfunction within inhibitory brain circuitry, particularly during symptomatic states. This model may help to explain why some addicts lose control over their drug use, and engage in repetitive self-destructive patterns of drug-seeking and drug-taking that takes place at the expense of other important activities. This model may also have clinical utility, as it allows for the adoption of treatments effective in other disorders of inhibitory dysregulation. (Author' s abstract)