This is an 8 week, outpatient research study testing the use of long-acting naltrexone (Vivitrol) as a treatment for marijuana dependence. Vivitrol is a medication that is effective in treating dependence on opiates and opioids, and in treating dependence on alcohol. It is FDA approved for these disorders. It is a long-acting medication that contains enough medicine in each injection to last for one month. One way it works is by blocking the effects of opiates, including opiates released by the body in response to drugs and alcohol. In this study, we are interested in testing the effects of Vivitrol in people with marijuana dependence.

Individuals participating in this study will receive two Vivitrol injections, each given four weeks apart, (week 1 and week 5). The injection is given in the muscle of the buttock on one side. Participants will attend clinic visits two times a week during this 8-week study for medical management for drug use and for monitoring of physical and psychological health.

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.

Inclusion Criteria:

• Between the ages of 18 - 60 years
• Meets DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, edition IV-TR) criteria for cannabis dependence
• Seeking treatment for cannabis dependence
• Reports using cannabis an average of 5 days per week over the past 28 days
• Capable of giving informed consent and complying with study procedures

Exclusion Criteria:

• Lifetime history of DSM-IV diagnosis of schizophrenia, schizoaffective disorder, or bipolar disorder
• Currently meeting DSM-IV criteria for a psychiatric disorder that, according to the investigator's judgment, may require pharmacological or non-pharmacological intervention during the course of the study
• Receiving opioid analgesic medication
• Known history of allergy, intolerance, or hypersensitivity to naltrexone
• Pregnancy, lactation, or failure to use adequate contraceptive methods in female participants who are actively engaging in sexual activity with men
• Unstable medical conditions, such as poorly controlled hypertension or liver disease, which might make participation hazardous
• Chronic pain conditions
• Liver dysfunction as indicated by elevated liver transaminases greater than 2 times the upper limit of normal
• Current DSM-IV diagnosis of substance dependence other than nicotine or cannabis dependence
• Legally mandated to participate in a substance use disorder treatment program
• Risk for suicide

8 weeks

Our study is open-label, uncontrolled and with a small sample size, and is not designed to test a priori hypotheses as to the safety, efficacy or effectiveness of our treatment intervention beyond its feasibility for further study.