We are testing the hypothesis that the medication baclofen reduces brain responses during marijuana cue exposure and/or craving in marijuana dependent individuals. Baclofen is FDA-approved for other uses, but not for the treatment of marijuana dependence. Functional magnetic resonance imaging (fMRI) will be used to measure the brain's response to marijuana cues. fMRI is a painless technique that takes special pictures of the brain (or other parts of your body). It does not involve radiation or injections.