With marijuana being legalized for medicinal and recreational use in more and more states, it will be that much easier for teens to obtain the drug, and scientists say states should consider the damage. Researchers from New York\u2019s Mount Sinai Hospital and the University of Montreal reviewed 120 separate studies pertaining to marijuana and its effects on the teenage brain, examining data on how and if marijuana acts as a gateway drug for harder substances. They looked at studies on how genetics and environment impact teen use of marijuana along with research into how the adolescent brain responds chemically to marijuana use. The study review found that not every teen who uses marijuana becomes addicted, and neither does every user experience the same negative effects. Some marijuana users, for example, experience serious psychosis while most do not. The scientists found that addiction and negative outcomes associated with marijuana use were most closely tied to the age when a person first used the drug, and those who began using as teens were most at risk. The earlier a person began using marijuana, the less likely they were to continue into higher levels of education, the more trouble they had performing adult roles and the more likely they were to experience mental illness. This, they concluded, was most likely due to the fact that using marijuana during adolescence could impair healthy development in key areas of the brain such as motivation, decision-making, reward, learning and formation of habits. Researchers determined that one out of every four marijuana users will develop a dependency, depending on genetic and personality factors. Teens with an inherited trait related to THC processing would be at increased risk for addiction. So too would teens with negative affect, impulsiveness or aggression. Actually, teens with these personality traits tend to develop a cycle of dependence wherein they use marijuana to medicate themselves out of these personality problems, which then tends to deepen their drug dependency and increases the likelihood of needing treatment to break their addiction. The study review indicates marijuana is not a benign drug, especially for teens and most especially for teens with predisposed genetic and psychological make-ups. Before any more states remove legal roadblocks to marijuana, careful attention should be given to the risks that teen populations in each state would face.