Cannabis use disorders are an important public health problem in the United States, but no effective pharmacotherapies are available to treat these disorders. The investigators intend to test a novel agonist pharmacotherapy, nabilone, for cannabis dependence and to study the relationship of this treatment with the brain using BOLD fMRI measures. The behavioral and physiological effects of nabilone and Δ9-THC overlap, suggesting that nabilone may ameliorate cannabis withdrawal symptoms while allowing treatment-seeking outpatients to benefit from medical management (MM) sessions when they are trying to stop using cannabis. The investigators propose to assess the relationship of nabilone, when added to MM, on cannabis use patterns in cannabis-dependent patients. The investigators also aim to determine the effects of nabilone on performance on neuropsychological tests and to assess the correlation of neuropsychological performance to brain changes using BOLD fMRI measures.