Marijuana (Cannabis sativa) is the illicit drug most commonly used in most Western societies [1]–[3]; it was consumed by at least 11.5% of individuals 12 years or older in the United States in 2010, even more so among teenagers (14%) and young adults (30%) [3]. Despite its common use, only a subset of teens and young adults using cannabis (25.4% and 19.0%, respectively) progress to abuse or dependence [4]. Such individuals become dependent on cannabis at a young age though cannabis typically has a delayed progression to dependence as compared to other drugs of abuse [5]. This difference in individual vulnerability has added to the heated debate as to whether cannabis is benign and should be legalized or a harmful drug whose status as an illegal substance should be maintained. Irrespective of the debate, cannabis-dependent individuals greatly outnumber those reporting dependence on other more addictive substances [3] and cannabis dependence carries a heavy burden, as it is associated with detrimental consequences on health [6]. Important research efforts have focused on cannabis use in association with specific disorders, such as psychosis,
