Study of Long-Acting Injectable Naltrexone to Treat Cannabis Dependence

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.