In this article, Kristen Weir examines the effects marijuana has on the developing brain. As more and more states are legalizing marijuana not only for medical but also recreational use, many doctors and psychologists fear the long-term effects. Many of the long-term effects of marijuana are still unknown, despite it being one of the most widely used illegal substances in the United States. Recreational use in states where marijuana is legalized only affects citizens aged 21 and older. Despite the age restrictions, some doctors still fear that legalizing recreational marijuana will allow the drug to become more accessible to young adults or teenagers. Susan Weiss, director of the division of extramural research at the National Institute on Drug Abuse (NIDA), expressed her concerns on the topic by stating, “There are many open questions…. But there is a growing literature, and it all points in the same direction: starting young and using frequently can compromise brain development." (Weiss). How does he recognize the fact that there is a "growing literature" when deals with marijuana use and its effects, also admits that new research all leads to the same conclusion, frequent use and starting at a young age can disrupt normal brain development The government and other private institutions are funding and researching these effects unknown. Medically, marijuana has proven to be a productive drug. Studies show that marijuana has helped deal with "pain, muscle spasms, seizure disorders, and nausea due to cancer chemotherapy." Scientist believe these benefits come from a chemical compound in marijuana called cannabidiol. This chemical is not the active chemical that gives marijuana users the mind-altering effects. ..the developing parts, the frontal cortex, are responsible for planning, judgment, decision making and personality. Adolescents also have to deal with the immaturity of their endocannabinoid system. This system is responsible for the psychological mechanisms that respond to the active drug marijuana, THC Krista Lisdahl, PhD, director of the Brain Imaging and Neuropsychological Laboratory at the University of Wisconsin, Milwaukee, says, “That (endocannabinoid) system is important for cognition, the neurological development, stress response and emotional control, and helps to modulate other major neurotransmitter systems” (Lisdahl). Frequent exposure to marijuana can “reduce cellular activity in the endocannabinoid system… This sets the stage for the which is why adolescents may be more sensitive to the effects of repeated exposure to marijuana, from a neuroscience perspective" (Lisdahl)