Marijuana is the most commonly used illicit drug, yet few clinical trials have evaluated
pharmacotherapy treatments for marijuana dependence. This study will evaluate the efficacy of
vilazodone for reducing marijuana use in marijuana-dependent adults. A contingency management
intervention (CM)and motivational enhancement therapy (MET)will be incorporated to encourage
study engagement and retention, and genomic DNA will be extracted to characterize subjects
according to polymorphisms of genes potentially relevant to the activity of vilazodone. It is
hypothesized that vilazodone combined with MET and CM will reduce the percent of
marijuana-positive urine drug screen results in marijuana-dependent individuals as compared
to a placebo treatment combined with MET and CM.