Study of Long-Acting Injectable Naltrexone to Treat Cannabis Dependence

This is an 8 week, outpatient, open-label clinical trial of long-acting injectable naltrexone as a treatment for cannabis dependence. The purpose of the study will be to evaluate marijuana use patterns and tolerability of long-acting naltrexone in 7 treatment-seeking, cannabis-dependent outpatients; also to assess feasibility of conducting a larger trial with this medication. Cannabis dependent patients will have twice weekly clinic visits where they will receive injections of Vivitrol four weeks apart, in Week 1 and in Week 5. The psychosocial intervention for this study will be Medical Management, designed to facilitate adherence to the study medication and monitoring procedures, as well as to support the participant in achieving his or her marijuana use goals. Participants will self-report cannabis use, will provide urine toxicology for quantitative assessment of THC (Tetrahydrocannabinol, the active ingredient in marijuana), and will provide serum samples for safety monitoring, and will answer questionnaires and will report on their physical and psychological health weekly.