Reduced response to reward in smokers and cannabis users

Background: Cannabis is one of the most commonly used illicit drugs. Reduced neural and behavioral reactions to reward have been demonstrated in other forms of addiction, as expressed by reduced mood reactivity and lack of striatal activation to rewards, but this effect has not yet been investigated in cannabis users. Methods: We hypothesized that cannabis users and tobacco smokers would evidence lower positive mood ratings in rewarded conditions than control participants and that this reduction would be greater in cannabis users than in smokers. We examined the influence of reward on mood and performance in a group of regular cannabis users, a group of tobacco smokers and a group of nonsmokers while they performed a spatial recognition task with delayed response that incorporated 3 levels of difficulty. Correct responses were either not reinforced or reinforced with money. We measured the accuracy of reactions, reaction times and mood ratings throughout the trials. Results: Cannabis users rated their mood as significantly worse than the smokers and nonsmokers during the easiest level of the rewarded condition. A significant positive correlation between mood ratings and monetary reward was found in the nonsmokers but not in the cannabis users and smokers. The groups did not differ with regard to task performance. Conclusions: Our results suggest that regular cannabis use affects certain aspects of motivation and that both tobacco smoking and cannabis use lead to similar motivational changes. However, the use of cannabis seems to affect motivation in a stronger way than does tobacco smoking alone.