The Reward System: What It Is and How It Is Altered in Cannabis Users

Cannabis is the most commonly used illicit drug, most often reported to be used for its euphoric and relaxing effects. It is suggested that cannabis’ interaction with the brain’s reward system in particular may be of specific relevance to both the euphoric and motivational effects of the drug and subsequently to the development of patterns of frequent, chronic use. Thus by understanding where and how cannabis acts on the system, insight may be obtained into whether and the extent to which cannabis has abuse liability from a biological perspective. Overall, research suggests that cannabis perturbs the brain’s reward system via its action on dopaminergic and glutamatergic functioning. In occasional cannabis users, THC acutely increases dopamine and glutamate throughout the system, which disrupts fronto-striatal functional connectivity at rest, and blunts the neural response to rewarding stimuli. However, the effects of cannabis on the reward system are dynamic and change over time, according to frequency of use. Chronic cannabis users display opposite changes in dopaminergic and glutamatergic neurotransmission, suggesting the development of neuroadaptations following repeated cannabis use. Studies also suggest that cannabis has abuse liability, with chronic cannabis users displaying hyperresponsive reward circuitry following cannabis-related cues and reduced neural markers of cognitive control over habitual behavior, and some mixed evidence exists for hyporesponsiveness of the reward system towards natural rewards. In light of the growing therapeutic and recreational use of cannabis, it is suggested that governmental bodies should implicate public policy to mitigate the possibility that individual cannabis use develops into addiction.