Interactions Between Physical Activity and Cannabis Use in Adults

In this study the investigators will explore the relationship between physical activity and cannabis use. The investigators will compare regional brain activation detected by imaging technique(fRMI) before and after exercise in cannabis users and compare results with results from controls. The investigators hypothesize that the regional brain activation in response to visual cues (pictures related to cannabis use and food) will be different in cannabis users than in controls and that exercise will significantly alter brain responses to the cues.