Imaging Dopamine Alterations in Cannabis Dependence

Cannabis is a commonly used substance, considered by many users as nonharmful. Cannabis interacts with the dopaminergic system at multiple sites in the brain and may lead to long-term effects that have been investigated in humans with positron emission tomography. In particular, since low striatal dopamine-2/3 receptor availability and low ventrostriatal dopamine release have been observed in alcohol, cocaine, and heroin dependence, multiple imaging studies have examined similar dopaminergic indices in cannabis dependence and have yielded various results. Initial studies suggested no abnormalities in the dopamine system in chronic cannabis users. More recently, evidence suggests that chronic, daily cannabis use is associated with alterations in the dopamine system; however, the regional topography of alterations differs from that of other addictions. We review these imaging studies here and discuss the factors that may have led to discrepant results, as well as the functional significance and public health relevance of a dopaminergic deficit in cannabis use disorders.