What portion of adolescents who regularly use marijuana develop a dependency on the drug?
Per a 2014 paper in the scientific journal Addiction: "In longitudinal studies, the risk of developing cannabis dependence has been estimated as one in six among those [regular] users who initiated in adolescence...." This amounts to 17% of users. The paper also documents that "regular cannabis use in adolescence approximately doubles the risks of early school-leaving and of cognitive impairment and psychoses in adulthood. Regular cannabis use in adolescence is also associated strongly with the use of other illicit drugs. These associations persist after controlling for plausible confounding variables in longitudinal studies. This suggests that cannabis use is a contributory cause of these outcomes but some researchers still argue that these relationships are explained by shared causes or risk factors."