Anderson DM, et al. - This study examined the relationship between marijuana laws and teen marijuana use. Medical marijuana laws have been passed in the United States by 33 states and the District of Columbia, while 10 states and the District of Columbia have legalized marijuana recreational use. Policymakers are especially worried that legalization will encourage youth use of marijuana for either medicinal or recreational reasons. Repeated use of marijuana during adolescence can lead to long-lasting brain function changes that adversely affect educational, professional, and social outcomes.