 The cannabinoid type 1 CB1 receptor is a protein found in the brain that is involved with the effects of marijuana; it may also play a role in the effects of alcohol dependence and withdrawal. Earlier animal studies have shown that although long-term alcohol use decreases the number of CB1 receptors in the brain, the number returns to normal after alcohol use stops. This study will use positron emission tomography PET and magnetic resonance imaging MRI scans to trace a radioactive chemical called 11CMePPEP, which can locate and measure the number of CB1 receptors in the brain. Researchers will study the CB1 receptors in the brains of people with alcohol dependence, and compare the results to the CB1 receptors in the brains of people without alcohol dependence. The results of this study will be used to further research into appropriate treatment procedures for alcohol dependence. 