University of Mississippi lab is home to the nation 's only legal pot farm . The Mexican government purchases marijuana , tests its potency . Study finds levels of psychoactive substances in pot on the soil . Mexican cartels control most U.S. pot , but it 's lower quality .
University of Mississippi lab is home to the nation 's only legal pot farm . The U.S. government grows marijuana , tests its potency . Study finds percentage of psychoactive ingredient in pot on the rise . Mexican cartels control most U.S. pot , but it 's lower quality .